I'm against religion because it's holding back the intellectual growth of humanity. It lets people be satisfied with mediocre ideas rather than actual facts.
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.