"You are dead wrong regarding most Christians believing the Genesis story is allegorical."
Actually, I don't think that's the case. The Roman Catholic Church, absolutely the largest denomination of Christianity has said that it does not think the 7-day Genesis account is literally accurate, and accepts evolution as the mechanism of speciation.
Perhaps you don't consider Roman Catholics to be Christians, but that's a big stretch. In addition, most mainstream Protestant churches also teach the allegorical nature of the creation story, and other stories like the noachian flood.
Beliefs vary among Christians regarding the literal acceptance of Old Testament stories, particularly of Genesis.