The people who don’t take part in any religion or who don’t believe in some higher being which commands their actions are more independent than people who do. When I say “weaker” in the question, I am referring to people’s mental or cognitive abilities, and how it would seem that people who don’t believe in God have better cognitive abilities than people who do.
The average religious believer, who goes to church every Sunday and reads a bit of the Bible every evening etc, does not really engage with what they believe in, in a way that “exercises” their cognitive abilities. Rather, they are fed this belief system or world-view and they passively absorb it into their minds, to the point where it is not questioned.
Now, in the case of people who have better cognitive abilities, such people don’t simply passively absorb information thoughtlessly, rather they have the ability to engaged and critically question the information that they receive.
Andy Thomson, the American psychologist said something like, it takes slightly more cognitive ability to renounce faith.
this is a very Illuminating speech by andy thomson:
http://www.youtube.com/user/richarddawkinsdotnet