If we want to believe that we live in a civilized society -- and I do! -- then murder's almost always going to be an inappropriate response. I have to say "almost", because I could imagine and sympathize with a case where someone killed the person who murdered a member of their family but walked on a technicality. Yes, killing the bastard would be wrong, certainly in the legal sense of the word. But I'd understand it.
To use a phrase that's been sorely overused lately, the decision to murder someone because you think that's the right thing to do is "above your pay grade". That's true for an abortion doctor, or a corrupt politician, or your selected scumbag of choice. Whether anyone is a scumbag or not is a matter of personal opinion. Those vary a lot, I've noticed. Heck, one man's corrupt politician is another man's beloved civil servant.
What's legal is not necessarily what's moral. And what you believe to be moral may not be what the fellow sitting next to you believes to be moral. And if you think something is legal, but immoral, you've got every right to try to use persuasion to get a majority (or possibly a super-majority) on your side in order to get those laws changed. That's true whether the issue is abortion, or gay marriage, or executive compensation, or campaign contributions, or your hot button issue of choice.
What you're not entitled to do is to use tactics that you would object to if they were employed against you. So if you think that you shouldn't picket an abortion doctor's house (which I agree with -- you shouldn't), you should be equally incensed when community organizers gather up bus loads of people to go picket the houses of AIG employees who received bonuses that they were contractually entitled to.
You don't get to throw paint on people because you don't like what they're wearing, whether that's fur or a t-shirt that expresses some sentiment that you find offensive.
You don't even get to throw a pie in the face of Bill Gates because you're tired of working on Windows Vista. I'm sorry, but that's just the way it is.
Nor do you get to hop out of the stands at Wrigley Field and charge the mound after Randy Myers gives up another homer to the opposition. But you do get to boo. It's within the civilized norms of behavior.
Yes, I've started out with the deadly serious and moved down to the outright silly and stupid.
But they're all on the same continuum.
We can all get along.
As long as we behave in a civilized fashion.
Once we decide what that actually is.