I think Paula Kirby put this aspect of christianity perfectly in her last Washington Post Piece,

Evolution poses a further threat to Christianity, though, a threat that goes to the very heart of Christian teaching. Evolution means that the creation accounts in the first two chapters of Genesis are wrong. That's not how humans came into being, nor the cattle, nor the creeping things, nor the beasts of the earth, nor the fowl of the air. Evolution could not have produced a single mother and father of all future humans, so there was no Adam and no Eve. No Adam and Eve: no fall. No fall: no need for redemption. No need for redemption: no need for a redeemer. No need for a redeemer: no need for the crucifixion or the resurrection, and no need to believe in that redeemer in order to gain eternal life. And not the slightest reason to believe in eternal life in the first place

For any christian to question the validity of Adam & Eve is to start on a very slippery slope.