One of the reasons I find it difficult to take militant atheists seriously is the quality of their arguments. I used to spend a lot of time discussing alleged inconsistencies in the Bible, and was used to all the examples they cited being rubbish. However, in academic circles, probably the most commonly cited "error" in the Bible is in Mark 2:26.
Jesus answered, "Have you never read what David did when he and his companions were hungry and in need? In the days of Abiathar the high priest, he entered the house of God and ate the consecrated bread, which is lawful only for priests to eat. And he also gave some to his companions."
Mark 2:25-26, NIV
The incident referred to is in 1 Samuel 21, where the high priest is Ahimelech. This is often cited as evidence that Mark got it wrong, and so when Luke and Matthew wrote their gospels later, they copied Mark but corrected his mistake by removing the reference to Abiathar. It is then used as evidence that Matthew and Luke used Mark as a source (which is quite possible - there is reasonable but not conclusive evidence that Mark was the first gospel to be written, and that it was based on the recollections of Peter, which would explain why it came to be the template for Matthew and Luke). It's also used as evidence that Mark is not a completely reliable source.
I'm studying 1 Samuel at the moment, so thought it would be a good opportunity to confront this alleged inconsistency and see if it actually stands up. It doesn't, of course.
The story continues in 1 Samuel 22. Saul finds out that Ahimelech helped David, and has that group of priests massacred. Well, all of them, except one, who escapes to tell David. Abiathar, son of Ahimelech (who then becomes high priest by virtue of being the only survivor). In fact, the conservation between David and Abiathar suggests that Abiathar had been there when his father had helped David (1 Samuel 22:22). Abiathar, being priest to David, ends up much better known than his father ever was. He gets 27 mentions by name in the Old Testament; his dad Ahimelech gets 11.
Mark records Jesus as saying that the incident was in the days of "Abiathar the high priest". Abiathar was not high priest at the time. On the other hand, he was alive at the time; he quite possibly witnessed the incident; he was the best known person there (apart from David) from the perspective of Mark's readers (and Jesus' listeners) 1000 years later; he became high priest as a result of that incident. I think that makes Mark's statement perfectly legitimate. After all, we'd be happy saying that William the Conqueror built up a large army in Normandy and then then invaded England in 1066, even though he wasn't called "the conqueror" until later. People don't seem to have a problem with saying that President GW Bush avoided fighting in Vietnam, even though he wasn't president at the time.
Once again, it looks as if whoever first came up with this as an objection to the reliability of the gospels was seriously desperate.