Looks like nobody has anything else to add, so I'll give a few of my conclusions, and maybe that will be the end, or maybe it will encourage additional input.
We seem to be dealing with two kinds of discrepancies: those within different copies of the same text, and those between different books covering common ground. In the first case, it looks like the best conclusion I can come to is that different texts became known and accepted with different churches in different regions. Once these texts became established in this way, they became resistant to change where they were known. This familiarity acted as a check against alteration, but as the books were circulated, changes crept in when they were copied outside the group that was familiar with them These altered texts survived to be re-copied many times, and even more changes were made. So now we are left with some diversity without knowing which documents go back at least to the original community. As for the latter case, where the books may have appeared to disagree (e. g., Luke and John), the texts were allowed to remain intact for the sake of harmony between the churches. The communities from which these books originated would not tolerate tampering with their text.
Certainly, all of us can accept that, regardless of who wrote the manuscripts, certain books with whatever their particular slants were accepted by certain communities or in certain regions (e. g., Matthew's work in communities with strong Jewish roots, Luke in Gentile communities or churches started by Paul, John in Ephesus, etc.) These may be seen as competing, but for those of us who accept there to be an ultimate Source common to all these texts and their inclusion into the canon, these are simply parts to the whole. We can talk of the teaching contained within a particular text, but it is also part of the whole Bible, and is properly understood when it is taken as part of the whole. Every writer had their part to contribute, and nobody had it all. This reflects the human element of the Scriptures—God worked with what the writers already had and what they could access. So he moved different people to make their contributions, and we benefit from having a bigger picture. Just as early Christians would have had personal visits from various apostles and their followers, now we have the writings left behind.
I've wondered why Jesus allowed so many differences within such a short time of his departure. I think it was to challenge his followers to find unity in love in spite of their differences. Certainly, there are some issues with which there can be no compromise, and the selection of some books for the canon and the rejection of others reflects that. Love of God is first—meaning faithfulness to the Supremacy of Christ and his teachings—but, love of neighbor—compassionate tolerance of other differences, even to the point of embracing diversity—must cover everything else. Splintered and divided, the church would not have survived. Embracing others and their contributions was part of the plan. It had to be because the early Christians, like us today, are so diverse in perspective.
That's my take on it, anyway. I know there are other ways of looking at this issue, but I wanted to make sure this way was represented.
Back to Dr. Ehrman...
In his book Misquoting Truth: A Guide to the Fallacies of Bart Ehrman's Misquoting Jesus (2007, InterVarsity Press), Dr. Timothy Paul Jones writes of his own struggle with the same issues Dr. Ehrman brought up. Ultimately, Dr. Jones came to entirely different conclusions than Dr. Ehrman. Dr. Jones agrees with Dr. Ehrman's observations that the texts have been altered. Where the disagreement occurs is with what its significance and meaning are. I find this to be the case with others who take issue with Dr. Ehrman's conclusions. (Other responses to Dr. Ehrman's book can be found in The Case for the Real Jesus, by Lee Strobel, 2007, Zondervan, and in The Gospel According to Bart, byDr. Daniel B. Wallace on the website bible.org at http://www.bible.org/page.php?page_id=4000). This is one of the fascinating aspects of the whole theist-atheist controversy—two people, looking at the same materials, can come to different conclusions. This is true in so many areas, from science to politics. I've been able to observe this first-hand in the jury panels I've served on. We would all have equal access to the same evidence, yet each individual would appraise its meaning and significance differently. We all have our reasons for what we accept and what we reject, and they clearly are outside of objective information.
Finally, to the texts that caused the problem for Dr. Ehrman...
I can see why some translations would render Mark 2:26 as "In the days of Abiathar the high priest..." It would not necessarily be to cover up an embarrassing error. Abiathar was far more prominent in the account of David's life than Abiathar's father Ahimelech. Hearers (and later readers) would recognize the name of Abiathar more readily, and it did happen in Abiathar's lifetime. I'm wondering something else, too. I'll assume that the translation should say "When Abaithar was high priest... ." From the account in 1Samuel 22:20-23, it would be easy to assume that Abiathar was quite young. (He avoided the slaughter of priests by Doeg on behalf of Saul, and escaped to tell David.) Since Abaithar outlived David, he was probably younger, but how much younger, we don't know, do we? Is it possible that we could have a situation similar to that of Annas and Caiaphas in John 18? Could Abaithar actually have been the high priest, but he was away at the time, and Ahimelech—formerly the high priest—was serving in that role in his son's absence? Granted, we may not get that from the text of 1 Samuel, but maybe this was known from some other source in the 1st Century AD. (I find it interesting that everyone who has addressed this issue assumed that the "mistake" was made by Mark. Since Mark was supposed to be quoting Jesus as related to him by Peter according to tradition, couldn't that also make Peter, or even Jesus himself, the source of error? I don't think the exemption of Jesus or Peter as suspects is due to any reverence, but, of course, to the questioning that this was actually stated.)
There are many possibilities, including a miscopying of the names of Abiathar and Ahimelech, which seems to have occurred elsewhere. In any case, it seems that, in itself, the suggestion by his professor was not significant enough to bring about the unraveling of Ehrman's confidence in the Scriptures. His present understanding of things seems to have been nearly a life-long process, and he may not be finished yet. I wonder if he questions every new conclusion, or if they just seem obvious to him. Frankly, I would like to go back to his experience all the way back in high school and the early years after that. I hope he does publish a follow-up book, and I hope he goes into more personal detail.
Thanks to all who contributed responses to this thread.
Regards,
Mike