Great food for thought...
I think you have all presented pieces of what is true...
As a Catholic turned Agnostic turned Buddhists, I know that even Tibet used to have a violent past... I have heard the Dalai Lama talk about this.
The Scandinavian countries today also have a different set of cultural codes than the ones they had as Vikings... and we can say they are the same set of folks, ethnically speaking, more or less...
So, maybe, we humans are evolving after all (I hope so!)...
I think that today's Buddhists that seem to be less violent than others are indeed so because the culture and the religion are intertwined: yes, it is a fact, some cultures are less aggressive and less confrontational. If their religion and their set of codes are aligned, that should be the result... at least, ideally.
Anthropologists have not reached agreement on this either, but it is possible that human nature has been more cooperative and peaceful than aggressive since we are Homo sapiens sapiens, contrary to what some European and American schools of thought have led us to think. History, with its account of battles, is not the best reflection of our real history as human beings. It is a partial and biased account of who we are and who we were.
Most indigenous cultures show a different picture: that everybody counts within a community.
It is a matter of what the starting point for each religion is, also... In Catholicism, we were supposedly expelled from Paradise for being bad folks... this is not the starting point of Buddhism...
Most Catholics do not practice in their personal lives what they believe - just ask the average Italian, Spanish, and Argentinian, and they will say that they will do all the social-religious ceremonies, but taking the religion as a guideline for daily life is a different thing... We never learned that it should be like that, either... I should clarify here: I am Argentinian.
As someone interested in Buddhism, I find that they say the opposite thing: if you believe that something is right, then you HAVE TO do it. Thinking and doing become one.
BTW, if any other people interested in Buddhism are reading this thread, I'd be interested to know if they recommend a teacher or temple in BA in particular. I've been looking for one, along either the Zen or Tibetan Buddhist lines, since I relocated here.