ooh.. do we want to have a moral argument about abortion?
Let's start with some points of (hopeful) agreement:
1. Women have the same right to liberty and freedom as men.
2. Contracting for a medical procedure is a private transaction that, in general, the government should not be involved in.
3. In order to make a moral argument at all, you have to accept that a life, before birth, has rights which should be protected by the state.
Almost all the debate over abortion, in western society, is centered around the third point. Sometimes there's some debate over the second point, but usually that's just in order to open the door for argument over the third point.
I'm not going to argue any of these points. Although I have good arguments for them, I think arguing these points is how to avoid having a moral argument about abortion. So let's just accept for the sake of argument that a medical procedure to abort a fetus is the taking of a human life and, like the taking of other lives, should be something the state should be concerned with.. and is interesting because in general the government shouldn't be involved in private contracts for medical procedures.
So when should the state take the side of a killer? The knee-jerk answer of "Never!" is clearly wrong. The most obvious example is self defense. I hope there's few who would argue that defending your person against external attack is much different to defending your person from internal attack. So let's consider the situation where a woman's person is clearly threatened by being with child. Personal opinion on the appropriate level of force that one can use to defend one's own person differs. My personal opinion is that no level of retaliation to those who initiate force can be considered excessive.. but I'm probably at the extreme end of the spectrum. Most others would say that if you can remove the threat to your person without killing then you should choose that option, and in the case of removing a fetus, sometimes that is a viable option, but often not.
Fundamentally, the moral question of abortion can be stated more generally: if you are responsible for the life of another, are you required to maintain that obligation? I hate to argue by analogy but I think this is one of the rare times where an analogy could help us remove emotion from our reasoning. Consider the man Bob hanging off a cliff. There's another man Aaron who has a firm grasp on his hand. If he lets go, the hapless hanger will fall to his death. Aaron figures he can hold on to Bob for quite some time and that he could eventually lift him. However, by holding on Aaron is causing himself quite a lot of physical pain.. and we can't ignore the significant possibility that Aaron will lose his hold on the cliff and fall to his death with Bob. Should Aaron continue to risk his life and cause himself significant physical discomfort to save Bob?
If you're a logical person, I think your answer to this question is predictive of your interest or attitude toward abortion.