My thinking is, if you are stupid (or ignorant, or irrational, or whatever) enough to be a creationist, you are probably also stupid enough not to know the high-order strategy for the prisoner's dilemma, and therefore cooperating with you is useless. You'll make your decision about whether or not to cooperate based on whatever stupid criteria you have, but they probably won't involve an accurate prediction of my decision algorithm, because you are stupid. I can't influence you by cooperating, so I defect and save some lives.