I would instead argue that pro-lifers appeal to a broader morality. It is futile quoting Bible verses to non-Bible-believers. But most people generally agree that it's bad to kill innocent people -- a MORAL, not logical, position. So we should start from there. Show, using biological fact, that abortion is killing an innocent human being.
Great point, all around.
Bingo! Nothing can be separated from our philosophy, whether that philosphy is right or worng.