Was Jesus an Historical Figure?

is this some sort of joke?

"The titles "According to Matthew," etc., were not added until late in the second century."

That really is only a half-truth mr. Zindler. As Bauckham notes in "Jesus and the Eyewitnesses, the Gospels as Eyewitness testimony", there really is no way the Gospel recipients did not know who wrote the Gospels. In works which are *internally* anonymous, the name was usually affixed to the outside of the scroll, probably on a seal. Combine this with the near-universal agreement among later Christians of the authorship, the evidence seems rather overwhelming.

"with Irenæus of Lyons, that we learn who wrote the four "canonical" gospels and discover that there are exactly four of them because there are four quarters of the earth and four universal winds."

I highly highly doubt that you would be able to provide a reference in Iranaeus' works which provides that argument. Maybe he was drawing coincidences between the four corners and the Gospels, but I highly doubt that he concluded that there were only 4 reliable Gospels on the basis that there are four corners of the earth.

"we come to the conclusion that the gospels are of unknown origin and authorship, and there is no good reason to suppose they are eye-witness accounts of a man named Jesus of Nazareth."

once again, the near-universal conviction of the later Christians seems to imply that the traditions are very old. Secondly, if the Gospels were not written by eyewitnesses, they're still reliable because, as Bauckham has exhaustively demonstrated, the Gospel tradition is extensively rooted in eyewitness testimony.

"At a minimum, this forces us to examine the gospels to see if their contents are even compatible with the notion that they were written by eye-witnesses. We cannot even assume that each of the gospels had but one author or redactor."

The New Testament has an incredibly wide textual basis (dozens of ancient manuscripts, 2 independent lines of manuscript tradition from before the 3rd century), unless you have manuscript evidence that there were later redactors, we have to assume that they had only one author.

"Both writers plagiarize (largely word-for-word) up to 90% of the gospel of Mark"

I wish to give 3 counter-points
1: Who is mark? mark was a student of Peter as Papias notes. Mark's testimony would have been invaluable in writing a life of Jesus
2: No one here is claiming that Luke was an eyewitness
3: Gregory Boyd and Paul Eddy have argued that Matthew and luke did not actually borrow from Mark, but given the primarily oral environment of the first century, they probably had access to the same traditions being retold around Christendom.

"to which they add sayings of Jesus and would-be historical details."

If you are saying that they fabricated sayings and details (and the tone seems to indicate such), then this is a positve claim which requires positive evidence. As Christopher Hitchens once said, claims which can be asserted without evidence can likewise be dismissed without evidence

"Ignoring the fact that Matthew and Luke contradict each other in such critical details as the genealogy of Jesus - and thus cannot both be correct"

ROFL. The geneology of Jesus is by no stretch of the imagination a "critical detail". at the very best it is an incidental detail which indicates independent streams of tradition.

"A real eye-witness would have begun with a verse reading, "Now, boys and girls, I'm gonna tell you the story of Jesus the Messiah the way it really happened..." The story would be a unique creation."

once again, Mark's testimony=Peter's testimony. Peter was a member of the INNER CIRCLE. Matthew and John the Elder were not part of hte inner circle.

"It is significant that it is only these two gospels that purport to tell anything of Jesus' birth, childhood, or ancestry."

Yes it is significant because as Burridge notes, it is but one factor which places the Gospels firmly in the bios genre. That alone gives us a nice a priori reason to trust their reporting.

"Both can be dismissed as unreliable without further cause."

I would strongly suggest you read "The Jesus Legend" by Paul Eddy and Greg Boyd, and "Jesus and the Eyewitnesses" by Richard Bauckham if you seriously think that mere doubt as to eyewitness authorship casts serious doubt upon the Gospels.