Why the analogy to slavery, or Hitler? It's inflammatory, and rarely advances the debate. Such analogies too often degenerate into "Hitler was a vegetarian too, you tofu-eating Nazi!!!*"
But in this case, I think the analogy to slavery is important, for two reasons. First of all, it was the last time we had an extended, society-wide debate about personhood. And second of all, as now, there were structural political reasons that it was much harder--nearly impossible--to change slavery through the existing political process.
Listening to the debates about abortion, it seems to me that really broad swathes of the pro-choice movement seem to genuinely not understand that this is a debate about personhood, which is why you get moronic statements like "If you think abortions are wrong, don't have one!" If you think a fetus is a person, it is not useful to be told that you, personally, are not required to commit murder, as long as you leave the neighbors alone while they do it.
Conversely, if Africans are not people, then slavery is not wrong. Or at least it's arguably not wrong--if Africans occupy some intermediate status between persons and animals**, then there is at least a legitimate argument for treating them like animals, rather than people.
The difference between our reaction to the two is that now we know Africans are people. It seems ridiculous to think that anyone ever thought they might not be people. They meet all the relevant criteria for personhood in twenty-first century America.
But of course, those criteria are socially constructed. The definition of personhood (and, related, of citizenship) changes over time. It generally expands--as we get richer, we can, or at least do, grant full personhood to wider categories. Except in the case of fetuses. We expanded "persons" to include fetuses in the 19th century, as we learned more about gestation. Then in the late 1960s, for the first time I can think of, western civilization started to contract the group "persons" in order to exclude fetuses.
But that conception was not universally shared. And rather than leave it to the political process, the Supreme Court essentially put it beyond that process. Congress, the President, the justices themselves, have been fighting a thirty-five year guerilla war over court seats. Presidents try to appoint candidates who will support their theory of Roe, Congress strategically blocks change, and the justices refuse to retire until they know they will be replaced by someone who supports their side. To change the outcome, a pro-life political coalition would have to gain a supermajority in Congress for twenty years--long enough for a few liberal justices to die in office.
It is theoretically possible that this could happen, just as it was theoretically possible to come to some political accomodation over slavery. But a combination of supreme court rulings and the peculiar federalist structure of American meant that the only way for either side to gain decisive results was violence. At every turn, the pro-slavery forces no doubt slyly congratulated themselves on their political acumen, while also solemnly and sincerely believing that they preserved an important right. But they made war inevitable.
If you interpret this murder as a political act, rather than that of a lone whacko, than this should be a troubling sign that the political system has failed. So why do so many people think that the obvious answer is simply to more firmly entrench laws that are rightly intolerable to someone who thinks that a late term fetus is a person?
I am accused, in the comments of Hilzoy's post, of loving violence and terror. Well, call me a terrorist sympathizer, but I believe that most terrorists do what they do because they, at least, genuinely believe that there is no other way to seek justice. Indeed, they are usually right, for all that I radically dissent from both their idea of justice, and their right to seek it through violence. But I am also humble enough to recognize that my own morality on a topic like abortion is constructed in context of two important facts: virtually all my friends are pro-choice, as is the social milieu in which I was raised, and a lack of access to abortion would significantly restrict women's autonomy.
These are not bad arguments in favor of abortion--I think modern America is more right than not about most moral questions, and the right to bodily integrity is important. On the other hand, in the face of fetal personhood, they are not very good arguments either. My parents significantly restrict my autonomy by continuing to be alive--if they died, I would inherit some money, which would increase my choices. But I still shouldn't be allowed to kill them in order to collect my inheritance--a moral insight which seems to be much more obvious and fundamental, I might add, than the wrongness of slavery or the rightness of abortion. Every society I know of forbids slaughtering your parents.
(Not that I want to, I hasten to point out. Hi, Dad! We're pricing out a nice GPS for father's day!)
I am aware that I have constructed my beliefs about personhood in the face of these things--like any good undergrad, I know the answer I need to reason to in order to ensure both social comfort and maximum personal freedom. I like to think that I am too rigorous a thinker to be seduced by such ephemera. But I am also aware that a lot of very fine thinkers were seduced into reasoning that Africans weren't people. Whatever evidence they thought they had, we're pretty sure how they arrived at their conclusions: African personhood would have caused enormous personal and social upheaval. Thousands of their friends and family would have personally suffered enormously without their slave wealth. Ergo, slaves weren't people!
And if I look at my own reasoning, well, frankly, it's not even reasoning. I've never sat down and thought, "how do I know that Africans are human beings?" I know. And I'm enough of a Chestertonian to be okay with that way of knowing. But presumably if I'd been raised in 1840 Alabama, I'd know just as certainly that they weren't.
Perhaps I find the certainty of the pro-choice side so disturbing because it feels a lot like the certainty of the warbloggers in the run up to the Iraq invasion. As some of Hilzoy's commenters point out, I was myself too caught up in it, which makes me cautious of getting caught up again. The pro-choicers seem to be acting as if people who shoot abortion doctors are some weird species of moral alien, whose actions can only be understood in Satantic terms, and who cannot and should not be negotiated with, because they only understand raw displays of power. Yet it seems to me that if I were in a society that believed fervently in the personhood of a fetus, I would very possibly agree, and view Tiller's murderer the way I'd view someone who, say, assassinated Mengele.
I realize that this opens many other questions, like "What does it mean to have access to the political process?" and what constitutes personhood. But I remain stuck with a fundemantal problem: I can understand their moral logic. When someone whose moral logic I can understand, even endorse (without endorsing the underlying judgement about the personhood of the fetus) is driven by that moral logic to kill, I think there may be a problem that society needs to solve. When more than one kills for the same cause, I assume that there's a structural problem in the political process that needs to be fixed. I'm not saying the violence is okay--I think Tiller's murderer needs to go to jail. But like many contributors to Obsidian Wings, I can understand the structural forces that contribute to Palestinian terrorism without believing the terrorism is legitimate. Unlike them, apparently, I don't find it all that hard to transfer that understanding to the fringes of our own democratic system.
* Sadly, I'm not even joking--see my old vegan threads
** Go ahead. I triple-dog-dare you to quote me out of context