Prolifers don't even have a coherent argument.
First, they assert that life begins at conception. Therefore, abortion is murder.
Then (other than the extremist fundies) they make exceptions for rape and incest. Tell me, if it truly is murder, why would it ever be justified? Just because that nine year old was raped doesn't mean that the fetus that did nothing wrong should be killed. Right? If it truly is murder, I would argue that the fetus' right to life outweighs any circumstance of birth.
You don't get to have your cake and eat it too. You're either justifying murder of an innocent fetus that had nothing to do with its creation or you're not.
Or... maybe it isn't at all comparable to murder and you're all retarded.