Theism: mental illness?

(New: audio version!)
Question from Devilush:
Do you agree with the studies that have been done stating that theism is similar to mental illness?

Answer by SmartLX:
I can’t actually find the studies you’re talking about. The Rational Response Squad talked about “curing the world from the mind disorder known as theism,” but they backed that up with their own arguments as opposed to actual studies. If you know of any, comment and link to them.

Theism is compared to mental illness (usually by atheists) because it involves believing in entities and events for which there is no physical evidence, scant documentation and no known natural explanation, which means it can be and has been called a delusion. The thing is, being deluded about something (which simply means misled) isn’t the same as being clinically delusional.

The big difference, for me, is that we get religion primarily from external sources. People are told what gods or equivalent beings supposedly exist, and by and large they accept the core dogma as is. There’s no particular mental illness that causes this to happen; it’s just believing what you’re told. A real mental case, on the other hand, invents as much incredible information as he or she adopts.

That brings me to an important distinction: I don’t think theism is a mental illness per se, but there are mentally ill theists out there. Further, there are many mentally ill people whose deranged thought processes are centred around religion, from those who think they’re Jesus to those who see demons everywhere to those who hear God telling them to kill people. Sure, some of these folks might actually be telling the truth, but since many contradict each other (there are several self-proclaimed Jesuses about, for instance) some of them must be wrong.

There’s plenty of criticism to level at theism based simply on the idea that it’s most likely wrong, it has no unique benefits and it’s potentially very dangerous. Questioning the sanity of all its adherents is no way to convince them of anything, and it seems to be a step too far anyway.