
The issue I think for many atheists is that they believe that their lack of belief in any religion gives them a theoretical leg up on the common man. They want to claim to be more rational and have none of the propensity for violence as they find the locus of most violence to be stemming from religion.
I find that to be silly because by simply being human you have the same propensity to commit acts of violence and aggression as anybody else. Being atheist does not make you a separate species.