Why can't we accept one another???

I am an atheist. I must confess that I have read many hateful posts by other atheists against Christians. I have seen both Atheists and Christians bicker back and forth with eachother over things that just arn't worth arguing about. Why do so many people feel the need to insult those who will not believe as they do. Can't we just have our beliefs and leave it at that???? I get tired of hearing Christians call atheists immoral and Atheists calling Christians stupid. As long as their not physically hurting you, why not just leave them alone or simply ignore them.