Many studies have also linked the ability to believe in religious/supernatural matters with either neurological difference or mental health issues with neurological origins. Studies have shown that certain areas of the brain in people with religious belief either work differently, do not work, or work where it has stopped working in the minds of adults (but still in children), than in the minds of people who do not profess to having any religious or supernatural beliefs. All these areas link to rationality, suspension of disbelief, sequential (linking) processing, sophistication of perception, ability to understand nuance, gullibility and susceptability and so on.
Misconceptions about mental health make many people take offense at the term. But to have some mental health issues is far more common and normal than to not have. It also does not mean that people cannot live roch, fullm productive, happy lives, or even acheive excellence and benefit mankind. Many of the world's greatest figures have suffered mental health problems, and, in fact, much of what they achieved was because of their issues: Mozart is now considered to have been bipolar (as well as having Tourette's), and his genius was achieved in his manic phases. Shakespeare suffered from deep depressions, which is where he sourced many of his most profound insights into the human condition. Many of the great female mystics, such as Julian of Norwich, suffered from anorexia, and were in heightened/disturbed states when they had many of their 'visions'.
As for great figures of the past all being religious, this is a spurious and amateur point of debate: in the past, it was often actually illegal to not be religious, and there was no other framework for people to think or act outside of. Moral, compassionate works were done in the name of religion because there was not other way in which they could be done, or described. Artists, and others, had to produce work that fitted in with 'allowed' forms of art, or what their patrons paid them for, which was either portraits or religious depictions. Scientists were forced away from any work that might threaten the notion of God. And many people were executed,barred or shunned, their work destroyed or forgotten, who stepped outside these narrow religious frameworks.
People really need to understand wider contexts if they are going to start opening up debate into these sorts of realms.