I've been trying to find something original to say about the assassination of George Tiller. That this is an act of domestic terrorism seems indisputable. That this terrorism was egged on by a major media corporation, Fox News, is also indisputable. It also seems very likely that the suspect Roeder had assistance from Operation Rescue, making the event the fruit of a criminal conspiracy, and that he had financial backing from someone, since he had about $10 to his name.
But if you are an anti-abortion crazy, this terrorism is supposedly justified to stop the greater harm of murdering helpless infants. Now, for the purposes of practical politics I take the standard liberal position on abortion, but in terms of theory I find the question (to use my favorite word) interesting, because the situation of a pregnant woman simply doesn't fit into the framework of individual rights that underlies liberalism. A pregnant woman is not an individual, but a system of one full-fledged person and some fraction between 0 and 1 of another person. And that's not even considering whatever rights and responsibilities the father might have, that's a whole additional kettle of worms. Fetuses (and post-birth dependent children as well) simply do not fit neatly into simple legal and moral categories.
Let's dig into the anti-abortion position a bit deeper. It has the virtue of simplicity: any fertilized zygote, any cell with roughly 46 human chromosomes, is a full-fledged person, and killing one is murder. No troublesome ambiguity or middle ground. Unfortunately, it is easy to show that the anti-abortonists do not actually hold this position. In practical terms, they follow the same common-sense mental schema that everyone else does -- a zygote is not a person, but a quasiperson or potential person, that does not enjoy the full suite of attributes that come with personhood but instead gradually achieves them during development.
I've argued this before by pointing out that roughly half of all fertilized eggs fail to implant and are ejected with the menses. If zygotes were people, this would mean our infant mortality rate was 50%, and that priests would be sifting through discarded tampons with a microscope looking for blastulas to say prayers over. In fact, this doesn't happen, and nobody would consider doing it. Thus, nobody actually considers that zygotes and blastulas are people.
But the Tiller murder made me think of an additional support for this proposition. If full-blown personhood starts from conception, and there is no moral difference between abortion and murder of an adult, then there is also no difference between a late-term abortion of the kind that Tiller specialized in, and an earlier one. But somehow the anti-abortion terrorists singled out Tiller as being uniquely evil due to his willingess to perform late-term abortions. This is further evidence that the anti-abortion radicals do not really hold to their professed ideology. In fact, if you really believed that all fetuses and embryos were equal, Tiller's actions would be marginally more moral than other abortionists, since most of his procedures were performed out of medical necessity.
So moral prescriptivism aside, from a purely descriptive stance zygotes and other pre-birth forms of the human organism are not treated as people, even by those who hold an ideological position that defines them as such.
[update: Here's a good post that makes the same point in passing; and also includes some interesting facts on the frequency of late-term abortions (they're very rare, about .01% of all abortions performed).]