I believe religion is a mental illness.
Let me elaborate why, and it really is simple. I suffer from depression, so I have a mental illness. This means if I do not take care of myself I will think irrationally and maybe do something stupid like off myself. So I am taking responsibility for possible irrational actions.
In the same way if you are a theist, you believe in irrational things (like hell and god) and you should be responsible for your actions. My depression can lead to irrationality, and religion can lead to irrationality. So they are the same thing.
Some people may scream now "but religion can lead to positive things". This is true, just as it is true that great things have been done by severely depressed people. Here are a few examples below.
Oh......and this guy below was important in defeating Nazi Germany.
So in conclusion religion is a mental illness. But then again that's just my opinion when I look at the major disagreements.