Serious question, if you're pro choice as we know it today, what makes you against this after birth abortion? In other words, what logically makes one OK, but not the other?
Not a troll question, as much as it sounds like one, I am just rolling the idea around in my head, and not coming up with much.
First, let me qualify that I don't support late term abortions. Fortunately, the vast majority of abortions are performed in the first trimester (12 weeks), and very, very few are performed after 20 weeks.
There are a few differences I see between "after birth" abortion and early term abortion. An infant does exhibit signs of thinking and feeling that an early term fetus would not, especially in the first few weeks. There is potential for suffering and human euthanasia is hardly guaranteed to be painless. So I have empathy for one's potential suffering and termination of thought because I find meaning in these things. I don't find similar meaning in an early term fetus.
A born baby also has interacted with people in a way that their termination can impact them, particularly the mother whose physiology naturally bonds her to her baby - these bonds are much more likely to be well formed for an infant and mother than an early term fetus.
Finally, there's the matter of viability and burden. Allowing an unwanted fetus to grow places burden and even risk on the mother (although not very high in developed nations). The newborn, on the other hand, can usually be surrendered to the state without becoming a further burden on the mother.