I'm against religion because it's holding back the intellectual growth of humanity.
Atheism proposes positive disbelief rather than the mere suspension of belief. I find it so annoying when people say atheism somehow requires faith. After all, you only need faith when you're talking about something that's in NO WAY verifiable.
Something like a God.
If you're going to tell me that a God exists, you've got to show me some actual proof of his existence. Otherwise, I've got no reason to listen to you.