I admit I am a bit opposed to abortion, but it's not for religious reasons at all. (I just happen to be Catholic - even if I was an atheist I'd still be pro-life). I think that abortion should only be given if absolutely necessary (like if the baby or the mother is in danger, or if the baby was conceived in a way it shouldn't - like if the mother was raped).
Actually, a lot of the people in the pro-choice movement are former Catholics. Margaret Sanger was one such person (though she went too far in the other direction with her racism and support for eugenics).