This is a very difficult question, the whole idea of how to maintain a sense of peace amid violent or hostile influences. It does seem justifiable to fight back with violence if one's life is threatened and this is the only way to fight back; but regardless of the reason for the expression of violence, it seems to alter the person or group of people who expressed it, however unwillingly.

I guess the peaceful purists would argue that self-sacrifice is the way to go, rather than give in to violence. Thinking about what I would actually do if, say, someone intended to kill me but I had the opportunity to kill the other person first. Would I do it to save myself? I don't think I'd really know what I'd do until the situation presented itself. I mean, I think I would, if I had to, but maybe there would be a way to engage the person in a conversation or distract him/her somehow. I don't know.

This reminds me of a question I've heard of that is put to men attempting to file as conscientious objectors in wartime. I can't remember exactly how it's worded, but the idea is that if you were to witness your mother being attacked and the only way to stop the attacker from murdering your mother were through some form of violence, would you take action? If the answer is yes, then you can't get the C.O. classification because you aren't 100% morally opposed to the use of violence.