Obviously the anti-abortion position is untenable, and so I would like to introduce a more interesting debate.
The famous developmental psychologist Jean Piaget studied the emergence of self-consciousness in children, and found what we call self-awareness generally develops, at, say, twenty-three months. I find this important when one considers precisely why the anti-abortion opinion is so indefensible. The anti-abortionist presents a fetus (or, in some cases, an embryo or even a blastocyst!) as something essentially human, and therefore due the protections we as society afford to all humans. Yet this is wrong, because genetics alone cannot make a human, for example my skin cells have the right genetics but quite reasonably no one would mourn their loss. "Potential" to be human, perhaps, is what endows the fetus with humanity? No, because sperm and eggs are not considered human, despite their potential as well. Of course, whether or not the sperm and the egg are joined is of no special importance, either, because this just puts the process at a stage later, and is not the end of the process. One does not simply fertilize an egg and then find the baby finished, because there are still many steps for the parent to consciously continue. At any rate, potential for humanity is not humanity itself. Finally, abortion is not immoral not because "it should be a woman's choice," that is absurd. Were one to grant the fetus the rights of personhood, its physical location does not deprive it of those rights, and except in cases where the mother's life is in danger it would not even be an issue as to abortion's morality or immorality. This debate entirely rests on what we consider human.
Clearly, then, it is self-awareness that sets apart the human from the non-, although of course it is a spectrum. But, if self-awareness develops so late, as Piaget tells us, we have to consider whether infanticide is a moral evil. Of course, this must be rigidly constrained: the parent and the state would have to consent, and a necessary precondition would have to be a battery of tests to make absolutely sure the infant is not self-aware. And this would still be fallible, so just in case we would have to set a limit well before Piaget's twenty-three months.
To me, this does not seem at all to be a moral evil. That is not to say I would be capable of doing it, as I probably would not be: a baby's cuteness is an excellent defense mechanism. At the same time, though, it is clear that abortion is not a moral evil, and in seeing that it is not because of the reasons I've suggested, infanticide rigidly constrained would not be, either. In fact, it might be on the whole quite the moral good: for example, in cases of congenital disease or even autism, where the state and the parents would otherwise be forced to spend a lot of money for no real net good.
Infanticide seems to me the next great moral question, and when society at large considers it I hope we will not allow our innate repulsion to color our moral judgments in an irrational way.
