The difference is that atheists mock instead of worship. Whenever they get together to relate their “disbelief”, it’s always in mockery, saying how stupid religious people must be to believe in some old white-bearded guy sitting in the clouds. Do religious people get together to say how stupid atheists are? No, and there’s the difference.
Maybe there is some kind of resentment. Not exactly the way I'd like to spend my day.
Other similar organizations — the KKK.
Religious people usually don’t get together to mock other religions either, the exception being Islam which often talks about beheading Christians in Mosque.