Some interesting points, thank you. Yes I agree that a lot of the Christians jettison what they disagree with and stick with the central tenant that they find most emotionally compulsive - that of the general notion of Jesus life and sacrifice, resurrection etc. I think many are willing to cut the arms and legs off their belief system as long as the beating heart of Jesus can be retained. In that way Christianity is resistant to being killed through appeals to literal thinking and rational argument. But for someone who does come from a literal understanding of the Bible, like Jehovah's Witnesses, I wonder if a loss of belief in Adam and Eve etc would be more destructive to their overall faith.
Suppose the Adam and Eve story was always known to be a metaphor, such that nobody thought to specify it when the story was told orally, as it was for hundreds of years before it was recorded in writing. Maybe the names Adam and Eve carry some connotation such that hearers always understood them to be archetypes, but that connotation has been lost to history.
I can kind of buy that. I have been reading that it is the Greeks who gave us a more logical rational approach but in fact the Israelite had no problem with contradiction - so perhaps they really didn't care whether Adam and Eve and the serpent were real. I would point out though for what its worth that Luke chapter 3 does list a chronology that goes from Adam to Jesus.