I do not consider it necessary that the gospels be written by their namesakes in order to consider them properly canonical and inspired by God. The major reason for looking at it this way is because the Gospels are not products of any one author. This is the way modern scholarship approaches the Gospels (see Luke Timonty Johnson--Ancient Christian Writtings). Due to the redaction process, and prior to redaction the fact that the Gospel material is extracted from an oral tradition which wound up in pre Markan saying sources, each Gospel is seen as the proaction of a community rather than an individual.
This communal authorship works both for and against an Evangelical position. Adjacent an Evangelical faith, it argues that the Gospel text is not inerrent, that it has mistakes and is transmitted by unknown persons whose identities cannot be pinned down. Indeed, to many atheists that's just the same as saying the authorship credentials are worthless and the Gospels cannot be verified. It works for an Evangelical faith commitment in that it grounds authorship not in specific personalities but in whole communities. The communal nature of early Christianity is well known, but often misunderstood. The transmission of the Gospel story is seen through the eyes of skeptics as the random transmission of wild rumors. Bautlmann's work on form criticism is understood as a condemnation to any eye witness appeal, and the Gospels are dismissed as a mass of unintelligible gibberish. But in reality, a lot of good work has been done on understanding early community as a controlled environment for the dissemination of information.
The best work for beginning this process of understanding is that of Oscar Cullman's The Johannine Circle(Philadelphia: Westminster, 1976) that first proposed the Johoninne community as a control environment, and much has been done sense then on that theme (see also:Robinson, James M. "The Johannine Trajectory," in: idem and Helmut Koester, Trojectories Trhough Early Christinity, Fortress Press 1971).A Doctoral dissertation at University of Dallas in the 1980s, The Mattrnew School, analyzed Matthew as the product of a community. When I say community I mean a commune. We know from Acts that the early Jerusalem church pooled their belongings and lived together and broke bread daily to study the teachings of Jesus and the OT prophets. Most scholars today argue that it was out of this time and place that the understanding of Jesus as messiah and his death as atonement were worked up and applied to the tragic events that galvanized the community of his followers, and having discovered this happy spin, some scholars argue, the resurrections stories for were forged. Of course that assumes the resurrection even didn't happen. On the other hand, there is no particular reason why one can't reverse the process; out of the realization of a risen savior the church used this communal structure to being a process of transmission which safeguarded the testimony of the community.
Oral cultures do not create oral traditions Willie Nile. Oral traditions are both constructed and passed on out of a very careful process. The passing of oral tradition is highly contextualized. They don't just allow anybody to stand on a street corner and make up some new story. Only officially recognized bards or story tellers can pass on the information. In cultures where the oral tradition is more than bardic, the information is relied through Rabbinical or other teaching authority. It is highly likely that the early communities, as they fragmented around Jerusalem, Samaria, and Antioch the verus members of that original community split off and went to live with the verus Christian communities. They guarded the transmission of the events surrounding Jesus' life and death and resurrection and most likely corrected errors of misspellings. The main thing is, this only had to go on for 20 years. After that point the testimony became written and the safeguarding was all in the test.
Of course I can't prove that this is really the way it happened. But it is most likely because there was a whole community, if we believe that Gospel accounts which witnessed the risen Christ and that's probably where Paul's 500 come in. This was the community Bethany where Jesus and his disciples stroll in the last couple of chapters of Luke just before the assignation. We also have a community in the Galilee where much of Jesus ministry took place, and we have one in Jerusalem where the last part took place. In each of these locations whole groups of people would have been part of the events and witness to Jesus preaching and teaching, and miracle working. It is the whole community of the early faithful that produced the Gospels through this process of oral tradition and redaction, and they were working from a carefully controlled process through which real eye witnesses corrected the mistakes of transmission.
Evangelicals do not like this idea because it departs from the old familiar truth tree. The truth tree was asserted by Josh McDonnell and seemed to give a much needed credibility to the Gospels. That was a major factor in getting my attention as a young college atheist, way back when. But the truth tree was an old argument which McDowell resurrected. It was first established by second century Orthodoxy and was never as clear cut and dried as McDowell would have us believe. Be that as it may, there are indications that some authoritative eye witnesses stand behind each of the Gospels, yet they do not have to be the ones traditionally assigned. For example, I am convinced that the author of John was an eye witnesses to Jesus life and ministry but that he was not the Apostle John. Clearly he was someone to whom the original community attached a great deal of significance, someone who had seen the original events unfold. The Elders of the community make a big deal out of who he was, and material of John is so heavily redacted it seems clearly to be the production of a greatly debated body of teaching that had been circulating through its respective community for a long time. I think the most likely candidate for authorial of the fourth Gospel is the Elder John of whom Papas speaks. He was a disciple although not the Apostle. He may also be the author of the epistles of John, who does call himself "the Elder." The difference in style is accounted for by the redaction process. the Elders of the community at the end of the book make it clear that they are compiling the teachings of this amazing person, this beloved disciple. So they are not recycling his words like notes at a college lecture. They are unpacking the summary of a very long and intenseness berate process that has torn a community apart. I'll say more on that but one can read about it on my John Page.
Matthew was most likely a narrativeal structure placed over the oriental saying source constructed by the Apostle Matthew. That can't be proven, but it makes sense given the testimony of Papias concerning the "loggia." But it is not necessary for the actual Apostle Matthew to have had anything to do with the book for it to be inspired. Even if we can't defend the specific personalities involved, there is no reason to about the basic information based upon the idea of community as author.
Evangelical apologists are sometimes uncomfortable with this notion of communal authorship. Some of them site the notion that its' too "liberal" (the evil buzz word). It caters to the enlightenment notion that the Bible has to have verification of logic, reason, and historicity. But when we look at what Evangelical scholars are doing, they are more often than not using these same ideas to verify the autoharp. That's why Layman is doing, and I dot' think he would have a problem with doing that, to the extent that it can be done; as I have no problem with asserting one's faith in the authorship of the namesakes. It's all a matter of what we think will reach people. I have never seen obscurantism reach any skeptic. It's true because it's the word of God and that's you need to know, is not a useful apologetic ploy. Either defending traditional authorship or not, I have no problem either way. But I dot' find it necessary to do so.
a more detailed expalination from my stie "Doxa."
Community as Author
We do not have to know the exact identity of the authors, because the original material comes from the community itself
A.Eye Witness check in Community.
B.Oral tradition was not uncontroled.
Oral tradition in first-century Judaism was not uncontrolled as was/is often assumed, based on comparisons with non-Jewish models. From pg. 53-55 in B.D. Chilton and C.A. Evans (eds.), "Authenticating the Activities of Jesus" (NTTS, 28.2; Leiden: E.J. Brill, 1998):
"...[T]he early form criticism tied the theory of oral transmission to the conjecture that Gospel traditions were mediated like folk traditions, being freely altered and even created ad hoc by various and sundry wandering charismatic jackleg preachers. This view, however, was rooted more in the eighteenth century romanticism of J. G. Herder than in an understanding of the handling of religious tradition in first-century Judaism. As O. Cullmann, B. Gerhardsson, H. Riesenfeld and R. Riesner have demonstrated,  the Judaism of the period treated such traditions very carefully, and the New Testament writers in numerous passages applied to apostolic traditions the same technical terminology found elsewhere in Judaism for 'delivering', 'receiving', 'learning', 'holding', 'keeping', and 'guarding', the traditioned 'teaching'.  In this way they both identified their traditions as 'holy word' and showed their concern for a careful and ordered transmission of it. The word and work of Jesus were an important albeit distinct part of these apostolic traditions.
"Luke used one of the same technical terms, speaking of eyewitnesses who 'delivered to us' the things contained in his Gospel and about which his patron Theophilus had been instructed. Similarly, the amanuenses or co-worker-secretaries who composed the Gospel of John speak of the Evangelist, the beloved disciple, 'who is witnessing concerning these things and who wrote these things', as an eyewitness and a member of the inner circle of Jesus' disciples. In the same connection it is not insignificant that those to whom Jesus entrusted his teachings are not called 'preachers' but 'pupils' and 'apostles', semi-technical terms for those who represent and mediate the teachings and instructions of their mentor or principal.
------------------ 22. O. Cullmann, "The Tradition," in Cullmann, The Early Church (London: SCM Press; Philadelphia: Westminster, 1956) 55-99; B. Gerhardsson The Origins of the Gospel Traditions (Philadelphia: Fortress, 1979); H. Riesenfeld The Gospel Tradition (Philadelphia: Fortress, 1970) 1-29; Riesner, Jesus als Lehrer.
23. Rom 6:17; 16:17; 1 Cor 11:2, 23; 15:3; Phil 4:9; Col 2:6-7; 2 Thess 2:15; 3:6; 2 Tim 3:14; Titus 1:9; 2 John 9-10; Jude 3: Rev 2:13, 24. Cf. Abot 1:1; Philo, The Worse Attacks the Better 65-68. 24. John 19:35; 21:24-25; cf. 13:23; 18:15-16; 19:26-27; 20:1-10; 21:7, 21-23. Cf. J. A. T. Robinson, Redating the New Testament (Philadelphia: Westminster, 1976) 298-311. 25. On parallels with other rabbis and their disciples and other Jewish usage cf. Mark 2:18 = Luke 5:33; K.H. Rengstorf TDNT 1 (1964) 412-43;.TDNT 4 (1967) 431-55.
Also, there wasn't an necessarily a long period of solely oral transmission as has been assumed:
"Under the influence of R. Bultmann and M. Dibelius the classical form criticism raised many doubts about the historicity of the Synoptic Gospels, but it was shaped by a number of literary and historical assumptions which themselves are increasingly seen to have a doubtful historical basis. It assumed, first of all, that the Gospel traditions were transmitted for decades exclusively in oral form and began to be fixed in writing only when the early Christian anticipation of a soon end of the world faded. This theory foundered with the discovery in 1947 of the library of the Qumran sect, a group contemporaneous with the ministry of Jesus and the early church which combined intense expectation of the End with prolific writing. Qumran shows that such expectations did not inhibit writing but actually were a spur to it. Also, the widespread literacy in first-century Palestinian Judaism , together with the different language backgrounds of Jesus' followers--some Greek, some Aramaic, some bilingual--would have facilitated the rapid written formulations and transmission of at least some of Jesus' teaching." (p. 53-54)
------------------ 18. Cf. Josephus, Against Apion 2.25 204: The Law "orders that (children) should be taught to read."; cf. idem, Ant. 12.4.9 209; Philo, Embassy to Gaius 115, 210, Further, see R. Riesner, Jesus als Lehrer (WUNT 2.7; Tubingen: Mohr [Siebeck], 1981; 4th ed., 1998) 112-15. 19. Jesus had hearers and doubtless some converts from Syria (Matt 4:25), the Decapolis (Matt 4:25; Mark 3:8; 5:20; 7:31), Tyre and Sidon (Mark 3:8; 7:24, 31; Matt 15:21).
N. T. Wright, critiquing the Jesus Seminar's view of oral tradition as uncontrolled and informal based on some irrelevant research done in modern Western non-oral societies writes:
"Against this whole line of thought we must set the serious study of genuinely oral traditions that has gone on in various quarters recently.  (p. 112-113)
--------------- 65. For example, see H. Wansbrough (ed.), Jesus and the Oral Gospel Tradition (JSNTSup 64; Sheffield: JSOT Press, 1991), referring to a large amount of earlier work; Bailey, "Informal Controlled Oral Tradition," 34-54. The following discussion depends on these and similar studies, and builds on Wright, The New Testament and the People of God, 418-43; and idem, Jesus and the Victory of God, 133-37.
"Communities that live in an oral culture tend to be story-telling communities. They sit around in long evenings telling and listening to stories--the same stories, over and over again. Such stories, especially when they are involved with memorable happenings that have determined in some way the existence and life of the particular group in question, acquire a fairly fixed form, down to precise phraseology (in narrative as well as in recorded speech), extremely early in their life--often within a day or so of the original incident taking place. They retain that form, and phraseology, as long as they are told. Each village and community has its recognized storytellers, the accredited bearers of its traditions; but the whole community knows the stories by heart, and if the teller varies them even slightly they will let him know in no uncertain terms. This matters quite a lot in cultures where, to this day, the desire to avoid 'shame' is a powerful motivation. "Such cultures do also repeat, and hence transmit, proverbs, and pithy sayings. Indeed, they tend to know far more proverbs than the orally starved modern Western world. But the circulation of such individual sayings is only the tip of the iceberg; the rest is narrative, narrative with embedded dialogue, heard, repeated again and again within minutes, hours and days of the original incident, and fixed in memories the like of which few in the modern Western world can imagine. The storyteller in such a culture has no license to invent or adapt at will. The less important the story, the more the entire community, in a process that is informal but very effective, will keep a close watch on the precise form and wording with which the story is told. "And the stories about Jesus were nothing if not important. Even the Jesus Seminar admits that Jesus was an itinerant wonder-worker. Very well. Supposing a woman in a village is suddenly healed after a lengthy illness. Even today, even in a non-oral culture, the story of such an event would quickly spread among friends, neighbors and relatives, acquiring a fixed form within the first two or three retellings and retaining it, other things being equal, thereafter. In a culture where storytelling was and is an art-form, a memorable event such as this, especially if it were also seen as a sign that Israel's God was now at last at work to do what he had always promised, would be told at once in specific ways, told so as to be not just a celebration of a healing but also a celebration of the Kingdom of God. Events and stories of this order are community-forming, and the stories which form communities do not get freely or loosely adapted. One does not disturb the foundations of the house in which one is living."[B.D. Chilton and C.A. Evans (eds.), Authenticating the Activities of Jesus (NTTS, 28.2; Leiden: E.J. Brill, 1998) p. 113-115.]
In addition to all of this we have corss referencing with the Pauline Corpus and with extra cononical sources. What all of this tells us is that the transmission process kept a stable and reiable body of inforiation in circulation to the time of writitng the texts. This time of texts Kosters places at AD 50 and Corsson and others back him on this. See Helmutt Koster's Ancient Christian Gospels for a brilliant exposition on these sources. What all of this amounts to is the unfolding of a complete defense of the historicity of the Gospels without the truth tree of torch passing from teacher to student. Becasue the studnets are the community tiself, and the community then becomes the teacher. But all of thse had to be kept in place only 20 years, and to that point eye witnesses would still have been alive. There is validation in the historical sources of the Pauline Cropus. IN other words we know there was a Peter, and Peter was a major player in the original events, he lived in Paul's time, met Paul and was able to relate his information to Paul. Thus the total body of sources backing the histoircity of Godples includes:
(1) Texts themselves
(2) community as author
(3) Pauline corpus
(4) extra cononical works themselves
(5) Pre Markan redaction refleted in readings of the Diatesseron
(6) works of Apostlic fathers.
If all of this seems far too empirically bassed for the pure of heart, it is the bread and butter of modern apologetics. In short, liberal textual ciriticism is useful. Stop throughing stones and start making use of it.