Murderous logic

In comments, Metavirus takes issue with the proposition that Tiller's murder being unjustified implies that abortion is not murder.  I attempt to explain further, and your thoughts would be welcome; I'd like to find some consensus.

Mark Thompson has an interesting related post at the League, where he explains Megan's position: believing abortion=murder does not justify the Tiller killing, but does make it understandable.

(Maybe it's interesting that the libertarians [Mark, Megan, and I] at least have that understanding and are interested in its implications for the political process, whilst the liberals [hilzoy, publius, Metavirus] are busier being outraged and wanting to deploy armed brigades to protect abortionists)

For the justified vs. understandable question, I think this depends on your assessment of the political process and alternative courses of action.  Mark and Megan go on to discuss how the Roe-Casey regime leaves anti-abortionists with virtually no political recourse.

So the question becomes: at what point, if any, does having virtually no viable recourse justify using violence to protect innocents?

Unless you're a nonviolent pacifist like Gandhi, I don't think the answer can be "never".  Most of us believe in self-defense: if someone is going to kill an innocent, we understand we would be justified in using deadly force to protect that innocent.

If you can get the law to do the protecting for you (via e.g. an official police force), that's preferable to vigilantism.  But when that's not available, most of us will consider taking matters into our own hands.   (and in particular we libertarians, being stauncher individualists and civil disobeyers, are more likely to be willing to do so than a statist or collectivist would be)