It's not acceptable when it's targetted terroristic violence from someone who claims to be on my side, and it's not acceptable when it's self-destructive violence by frustrated youth, or honor killings or piracy on the high seas.
No, I don't have a solution, just this minute. I just wanted to be clear on the concept.
Update: Oh, I forgot to mention torture. Torture's bad. The spectre of the President of my own beloved country trying to "carve out an exception" to permit the abuse of prisoners held incommunicado in secret CIA facilities while denying that we are applying torture as a national policy is just too much. It's weird and it's morally disgusting. Here's the deal: I will not ever give money to or vote for a candidate who in any way supports the use of torture. I will not give money to political parties which in any way support the use of torture. I don't care what party or position or identity you represent: if you support torture, you cannot represent me.