We can point to war or to the Stanford prison experiment. People in unusual stressful situations have the potential to be abusive, or to follow abusive orders.

But there's a large gap between that and the kind of trouble that results in serial killers. Soldiers in a war are under terrible living conditions, and commit atrocities in the name of taking it out on the enemy.

But even the soldier does not stoop as low as torturing animals. The enemy, maybe, but not the innocent. Serial killers are completely indifferent to the pain of the innocent. Soldiers only hurt the outgroup, the enemy.

And I think you're being unfair to people living in more primitive societies. There's crime in every society, but you will not make friends anywhere by being antisocial. A small village doesn't survive by people turning against each other. It would simply cease to exist.

My claim is that most people do not have the violent impulses, and don't need to channel them. Some people do. And they benefit from channeling them, because bad outcomes happen much more often to those who don't.

Nature will beat the violence out of people, over generations. You simply survive less in aggregate with a harmful set of instincts. Most people have no need for hard to control violent impulses, and indeed tend to be born without them.