You actually don't have a point...
...while I can agree some cultures may be more prone to violence I still don't see any evidence that culture specificity per se is the cause of violence. CI is actually right when he says it has happened everywhere.
Culture specificity may induce violent behaviour but violence is not born with culture alone. Human beings are genetically selected for competing and taking the opportunity when one presents itself.
This not to mention that "violence" is a very broad term that is not only restricted to killing. People are violent in the most varied possible manner even and often with loved ones. The problem of violence is better fitted in the context of power struggles to control the resources and ensure group dominance over other groups. We are by "design" gang people, and gangs, yes you guessed it right, do fight.
Nothing wrong with it prevented it doesn't become a social disease. US is a very good example of social violent culture and still I don't think sorting all the gun problem in the US would change human nature all that much.
Every country everywhere, has had in its past or present, very shady, very dark, moments, not because of culture specificity but because the opportunity to profit with violence was there.
As for cultures, they often the result of more profound causes then the causers themselves of anything, they reflect other elements at play often poorly identified. A good example of this is blaming religion and religious cultures for terrorism, when the actual cause of terrorism is way harder to pin point. A society that has for the most part dropped ethics and moral regarding industry, trading, and corporations behaviour at large, and in which the Law does no longer work to protect the citizen but serves corporate interests will have its feedback in violent terrorist behaviour, for one because it hits back and works. Curiously enough most terrorists are born in the countries they end up attacking. The wave of terror we live with is a cry out of no hope in any sort of dignified future that the latest generation of youth in its fringes degenerated into violent to the extreme behaviour. The difference between a terrorist and the "movement against the 1%" public riots, is that the other 99% in the riots shouting and kicking against the state of affairs of our world are not psychotic...psychotics now have the perfect world and instruments to justify their need for destruction.
Yes Historical opportunity generates violence, culture just feeds it.