> having a less violent society is very much an evolutionary advantage

I don't see how this is the case. We have a lot more violence than is necessary for adaptation or survival. I don't think our 'ingrained sense of fairness' is an advantage, I think it is similar to what already exists in nature, but is then broken down by our fragile emotional state and confused by our higher brain functions clashing with our evolutionary simple heuristics. It's like running a web app in AWS to control a shopping list and it's source code consists solely of algebraic expressions. It's cumbersome and problematic. I'm sure developing our higher brain functions was useful in our survival, but it clearly conflicts with our instinctual survival traits.