I'm really not sure that there are many people that are "pro-abortion" in the sense of thinking that an abortion is a good thing in itself. (Which is not the same as thinking that it might be the best, or least bad, option in some situations).
For myself, I think that there are some cases where abortion is the best option, but in most cases it is only the choice issue and a pragmatic preference for regulated and legal abortions over unregulated illegal abortions that lead me to favour the current situation (as it is in the UK) or something very like it.