I guess humans need someone to lead them, they need heroes, they need guidance. This is where religion and politicians take their power, they work out the best way to control the human masses, and do so with incredible simplicity and efficiency. They use simple ways to diffuse their memes that most persons accept with subservience. I am forced to reach the fact that humans are easy to manipulate. Human history is a violent one, tales of indescribable violence can be found in ancient and recent history.
Humans definitely have a natural tendency for violence.
The big question is the extension to which violence and peacefulness can be taught . I found some evidences that support the theory that, although humans have a natural violent instinct, their aggressiveness is mainly an environmental factor. I studied the history of a place called Tibet. As a conclusion, I think humans are as aggressive as they are allowed to be. They might have a natural instinct for violence, but when taught properly, they can become peaceful.