Right, birth control is basically a conflict between genetic and human interests. Short-leash genetic control is situationally triggered and can be difficult for our conscious mind to admit / predict ahead of time. We think we will have self-control, but when the time comes, the short-leash modules trigger and convince us to have unprotected sex (to advance genetic interests). Making it as easy as possible to not give in to short-leash temptation is important for resisting it, which is why keeping condoms around is better than abstinence, and an IUD or injectable birth control is better yet.

Admittedly there is some rationality to the idea of not just ameliorating temptation but avoiding it. Also I suspect abstinencers have a different utility function than I do - they view sex as bad in and of itself and not just because of consequences like unwanted pregnancies. Their method makes more sense given that viewpoint. If it worked, at least.