A friend asked me if violent opposition to abortion is legitimate in principle. Here's my response:
Before answering your question directly, I'd note that the point of my AHA post was not to expound my own position or discuss the issue on the merits, but to interpret Trewhella's actions/statements on their own terms, and consider if that's consistent with AHA's stated nonviolent philosophy.
I think there are situations where we can honestly say, "I wouldn't do it, but I don't blame someone who does." I'm not referring to this issue in particular, but generally. However, it's not incumbent on me to make Trewhella's (or AHA's) arguments for him.
For instance, years ago a convicted sexual predator was paroled. But someone burned his house down before he could move into the neighborhood. That's not something I'd do. But I don't fault the person who did it. And if I witnessed the person who did it, I wouldn't report him to the authorities. If the police questioned neighbors, including me, I'd feign ignorance.
On the substantive question, I'm inclined to say "no." I don't think vigilantism is wrong in principle. But I think there are are implicit parameters to permissible vigilantism. And like many ethical issues, it's hard to drawn the boundaries precisely. We have borderline cases. So I don't know that I can lay down an exceptionless generalization. I'll have to content myself with illustrations.
If I'm walking in the park, and I see a man attacking a woman, it's generally permissible, and sometimes obligatory, for me to forcibly intervene. Mind you, even that depends on other considerations. If he's 6' 4" and I'm 5' 5", my intervention would be futile, unless I have a gun.
Likewise, if I'm the caregiver for my elderly invalid mother, then I can't risk injury. In fact, I probably can't even risk a police investigation.
But as a rule, I'd be justified in counterattacking the attacker to protect the third party.
Keep in mind that even in that situation, I wasn't on the lookout for muggers or rapists to neutralize. I simply happened upon that altercation. I found myself in that situation. I didn't seek it out.
By contrast, in many parts of the world, innocent people are murdered with impunity. One country invades another country without provocation. Or you have a bloody civil war.
But I don't have a duty to hop on a plane, fly to that theater, choose sides, get a gun, and start killing the aggressor. Not only is that not obligatory, but I doubt it's even morally permissible. The enemy soldiers aren't my enemies. They are not a threat to my own family. It's really none of my business.
And I'd say the Bible corroborates this viewpoint. If vigilantism was generally obligatory, the Roman Empire afforded countless worthy causes. Yet Jesus, the apostles, and/or NT writers don't call upon Christians to practice frontier justice. For instance, Christ did not align himself with the Zealots, even though they had legitimate grievances.
Indeed, St. Paul implicitly discourages vigilantism:
11 and to aspire to live quietly, and to mind your own affairs, and to work with your hands, as we instructed you, 12 so that you may walk properly before outsiders and be dependent on no one (1 Thes 4:11-12).
1 First of all, then, I urge that supplications, prayers, intercessions, and thanksgivings be made for all people, 2 for kings and all who are in high positions, that we may lead a peaceful and quiet life, godly and dignified in every way (1 Tim 2:1-2).