There is a good reason why atheists are generally more peaceful than other people.
Atheists realize something important.
When you take mythical deities out of the equation, atheism is the great equalizer. We are all the same under atheism.
Different religions have different views about how to live life and more importantly how to achieve a good afterlife. They get mad at the other religions that try to tell them something different. This other news creates a cognitive dissonance, best resolved by shutting up the arguments you don't want to hear or burying your head in the sand.
But with atheism, everyone is in the same boat. That's just reality, and it waits for no man or woman, no matter how badly you try and avoid it. You live, you die.
This applies to everyone under atheism: This is the only life there is. There is no afterlife. So you'd better make the most of this life. You'd also better respect everyone else's right to maximize their potential in this life by helping people when you can.
If everyone just followed this simple atheistic belief system, the world would be Utopia.
It is only the belief in God and mythical deities that prevents our return to the Garden, because everyone is so busy trying to live like it says to in whatever Good Book they ascribe to, and silencing contrasting views (including atheism) through various violent and ignorant means.
Isn't that ironic?