Atheism leads to mental illness (and possibly is a mental illness) we can deduce this from all the atheists online who have such irrational hatred towards religious people.
Their behavior online gives us an insight into their mental health and it clearly isn't healthy, we can deduce this with the emotional rants and hateful things they spew about any who do not share their views. They also hold some irrational and schizophrenic beliefs i.e "all Christians are out to get us!!" and "all Christians oppose science!"
Their Christophobia and Islamophobia run deeps, it is obvious with all the anti-religious messages they post about these people.
Finally, studies have revealed that atheists abuse drugs more than religious people, suffer from more depression, are more likely to commit suicide, have anxiety issues and higher aggression levels.
(Studies: http://ajp.psychiatryonline.org/doi/abs/10.1176/appi.ajp.161.12.2303 and http://www.sciencedaily.com/releases/2013/10/131003093041.htm)
The evidence tells us that atheism is either a mental disorder or that the behaviour of many atheists often leads to mental illness.