It appears from all your comments that:
1. "Without evil, there can be no good" (quoted from Darth Enzo), which can be said about anything; if everyone was stupid, than no one would be stupid because 'stupid' would be normal.
2. We do not live in a perfect world so there can be 2 positions taken at the same time in this debate; non-violence in a perfect world, and violence in our own. Do you agree?
3. 'Justice', 'Vengeance', and possibly 'Pay-back' are all forms of justification for violence based upon statement 2's 'non-perfect world'.
Saying these things makes me wonder.....
If there can be no good without evil--then why couldn't there be no 'unjustified murder' if there is presently 'justified murder'. What I'm saying is if murder is murder, and the only thing seperating 'justified murder' from 'unjustified murder' is personal opinion and piece of mind......then isn't all murder the same, and using words like 'vengeance' and 'justice' are just defense mechanisms created by our brains to protect us from guilt?