Religion, to me, is merely a tool that our primitive, stupid ancestors to explain the things that science can definitively explain today. As far as we as a species have advanced, it puzzles me just why it retains such a strong foothold in modern society; one would assume it would be very obsolete in a world of such knowledge.
And I know some people practice religion for things like fulfillment, morality, etc. but I feel as though one can obtain these same things with science. What makes it so much more fulfilling to believe that the world was created by a god than to believe that it was created by the Big Bang?
Morality is a given no matter your religion. Few things upset me more than when people say that because I don't follow a deity, I have no moral code. I'm not going to up and kill a man just because God didn't tell me not to. The establishment of societal morals may have been assisted by religion, but after so many centuries of living with them they are so deep-seeded in our culture that, no matter one's religion, one has to follow them. I grew up with primarily atheist parents and I was taught much the same ethical code that would have been taught to the child of the most religious parents on the planet. Furthermore, history has shown that when God said "thou shalt not kill" he meant anybody who isn't anything other than Christian. There have been atheist murderers, without doubt, but throughout history Christians have consistently been genocidal dictators and maniacs, and they all claimed that they act in the name of God. What kind of good, loving deity asks you to kill in his name?
It also must be said that, as perhaps a risky generalization, atheists are generally less hateful, prejudiced, etc. than Christians.
I speak, of course, only of the die-hard zealots who follow the teachings of the Bible to the letter and unthinkingly act out everything the Bible tells them to do regardless of established morals. Christians don't bother me if they don't try to shove religion down my throat or wipe all the non-Christians off the world.
In conclusion, I am an atheist because I take comfort in that which can be scientifically proven, over that which was written in a book thousands of years ago. I do not accept many of the rash, evil doctrines put forth in that same book; note that I do not say that all the doctrines in this book are so.