The problem is that born vs. unborn may not be that big of a distinction as far as the child is concerned. A six-month preemie is born, but a nine-month, healthy baby still in the womb is not. By the logic of the birth distinction, it is immoral to kill the preemie, but perhaps not immoral to kill the nine-month unborn baby. Yet the nine-month is much farther along in development than the six-month.

Born-ness matters a lot to the mother, but it isn't very satisfying as a criterion for defining when a developing human ontogenetic process becomes a person in the meaning of the law, with its own independent right to life. And that is the issue that the anti-abortion people consider self-evidently paramount.