A neuroendocrinologist called Robert Sapolsky, a professor at Stanford University, is a self-described atheist.
When accepting the Emperor Has No Clothes Award in 2002 from the Freedom From Religion Foundation, which is given for recognition of "plain speaking" on the shortcomings of religion by public figures, he said:
I was raised in an Orthodox (Jewish) household, and I was raised devoutly religious up until around age 13 or so. In my adolescent years, one of the defining actions in my life was breaking away from all religious belief whatsoever.
He's also, during footage of one of his lectures, compared religion to a shared schizophrenia, argued that the behaviours exhibited by "prophets" in religious texts are diagnosable acts. He's also reasoned that the parables and teachings of these men - such as stories of the construction of the world in seven days, virgin births and burning bushes - are stories constructed by "extremely formative, extremely schizotypals throughout history".
He's argued that religious rituals are a form of exhibiting obsessive-compulsive disorders, and that religious people are on a spectrum of mental illness.
It's certainly a challenging viewpoint to anyone religious, but it's also an interesting lens by which to view the phenomena that has moulded societal constructs for millennia.
Or, if you're looking for a more frank, simple explanation as to the purpose and existence of religion, here's George Carlin on the matter: