I am an atheist, and there used to be another guy at my school who was atheist. He moved to Oregon recently, but before he left, we had a philosophical discussion on god(s) and things surrounding the idea of god(s).
One thing we noticed is this: neither one of us could think of a war that did not divide people on religion. We went to our history professors, only one of whom did not have a PhD, and they all reluctantly agreed with us that somewhere at the root of the conflict was religion.
There is always a feeling of the need to help the rest of the world by forcing one's religion down everyone else's throat. This is not always true for an individual, but as a group, religions have a history of this sort of thing turning violent. Just as the radical Christians went on Crusades, killing those who did not agree with them, the radical Muslims today are doing the same, killing non-Muslims.
Philosophically, everyone wants an answer in the universe. Even I occasionally utter something about God, as I used to be a Christian. The thing is, we tend to assume things, as a species. We have no real evidence for a God. Now, I do not claim there is evidence against a god either, but the truth is, we cannot know. In reading the Bible, I noticed contradictions, or inaccuracies, and that bothered me, eventually causing me to lose faith.
I have morals, to the disbelief of some christians around me, and I am understanding of others' religions. I respect every individual's right to his or her religion, and I respectfully disagree, citing lack of evidence. But in no way to I attempt to have everyone become atheist. The only time I argue against religion is if I feel I am having religion pushed onto me.
Congrats to everyone for keeping this a mature, intelligent discussion so far, normally that does not happen.