Atheism was actually becoming rather popular in the late 19th century. However, with the Theory of Relativity and the Heisenburg Uncertainty Principle, the rug of certainty and stability was pulled out from under the average person's life. To live with empirical science is to live with uncertainty and doubt. Not everyone can emotionally handle that. I've known several people who said that their "Gospel" must be true because it is too depressing to accept that it is not. Most religious people worship comfort and security more than they worship truth, let alone the thrill of discovery. Most people believe in what they feel good believing in. It is not really a matter of intelligence, but of emotional insecurity. Science is perceived as a threat, therefore it is a hoax.

People do not all / always share the same level of intelligence and perception capacity. Therefore, God/Religion in general is an easier answer to swallow by those who can barely think.