The reason atheists, or anti-theists more specifically, rag on religion is because of what religion as a whole is capable of doing. You don't have to look very far in the US to see how batshit crazy and influential Christians can be with their beliefs. You can replace Christianity with any religion and it wouldn't really make a difference, or any region in the world for that matter (Islam/Middle East). With few exception such as spiritual/nature based religions of the East religion is a plight on mankind. I am not against anyone who has spiritual beliefs or believes in "a" God, but that's about it.
We're talking about organized religion here. We're talking about people who think being an atheist means you don't have morals. We're talking about even the "nicest" of religions judging you and shunning you for your lack of identical beliefs (mormons). Plenty of good people are religious or believe in God, and plenty cherry pick the good and ignore the bad, which is fine -- I come from a Christian/arab family so I'm used to it.. but the fact is, I can't and will never respect the religious denominational beliefs anyone has. Whatever good it does is erased by the bad it does on a regular basis, like infringing on peoples civil liberties and breeding prejudice and hate.
Etc etc etc etc.