Axually, they ARE foolproof solutions. But like any other contraceptive, they don't work at all if they are not used.
It's sexist to believe that a woman should have the right to control her own body? I thought that was all the rage these days. If you absolutely, positively, don't want a baby, control your own body and absolutely, positively, don't engage in sex. Same goes for the man, for that matter--and I would say even more so for him, because he's not always afforded the same opportunity to decide if his accidentally-conceived child lives or dies.
If it's not sexist to allow the woman to control her own body AFTER conception, then it's not sexist to suggest that she control her own body BEFORE conception as well.