Why do some atheists judge religious believers so harshly?

Human Nature has given us all a need to be or feel as if we are superior to others. Because in modern culture we are no longer little tiny tribes fighting over who is superior, we wage will try and gain superiority through other means. Atheists, Christians, muslims agnostics and practically every other religion thinks that they are right. And they boast and look down on others that do not share their views. EVERY social group does this, to an extent. Appearance of superiority is mostly what it's all about.