Peter Enns' latest post suggests that he has identified the biggest theological objection to rejection of the historical Adam, the first man, specially created by God. Enns thinks that the biggest problem is the wrath of God. Adam's sin in the garden is important to explain why God's wrath is against the human race.
Obviously, I don't agree with much of what Enns says. As far as I am concerned, it seems pretty clear that he has rejected the Word of God, and consequently is outside the fold. Nevertheless, it is interesting to see which theological topics Enns thinks are most directly affected by a rejection of the literal sense of Genesis 1-2.