Give it enough time, and those with a propensity to whacking their own kids, will be outbred by those that don't. So, slowly but surely, abortion will become more and more scarce. God works in mysterious ways, after all.
The best those opposed to abortion can do, is to not do anything that stunts this outbreeding. For one, have a bunch of kids yourself. Teach them proper morals, as in: You have a finite capacity for helping others. Use it wisely, by helping those you find most worthy. Let the rabble sink under their own weight. If some whore kills of her children in fertile age, DO NOT ever support any mechanism whatsoever, by which she can lay claim to resources produced by other people's children. That way, once she is old and sick, she will also be gone. The quicker the better.
And lest anyone think this is just an excuse for selfishness, reread the part of finite capacity for giving aid. In a fertile world, there will always be more needy people than resources available to sate their needs. SO, it becomes a moral imperative to chose whom to help. And helping a childless-by-killing-her-kids-back-when-she-was-young-and-strong-enough-to-take-care-of-them, with resources that could otherwise be spent on helping a poor woman who may not be able to properly feed her child despite wanting to, is blatantly immoral.