Shrug.
Oh, no question, but that is not the point the article is getting at. There are, after all, many types of mental illness. The specific contention the article is making is that belief in something higher than ourselves is intrinsic to the Human condition, and therefore those who specifically deny the same are, in effect, denying a fundamental part of themselves.
I agree with the article (although calling non believers "mentally ill" as a conclusion is a bit harsh). There is a "god-shaped slot" in all of us, and without a belief in the divine it becomes a void into which all manner of crud gets thrown. When people stop believing in God, they dont just start believing in nothing. More usually they start believing in everything.