Hn, there's a bit of a strawman here, although maybe I'm wrong. I know very few people who've actually thought about it and still allow abortion and who think that "life begins at birth," for instance.

Most people I've talked to want to start requiring reasons for abortion fairly early, so there goes the problem with making an argument from person-ness. And I think there is a pretty obvious reason why birth is special when considering only the subset of abortions done for the health of the mother.