It seems to me that all religion, at least theism, is founded on one simple and often unexamined prejudice, which is the belief in the supernatural. This may sound obvious to an atheist but I am sure that many so-called "religious" believers would feel uncomfortable if it were pointed out to them that their whole faith would fall apart if they didn't believe in the supernatural. I believe it is almost certainly a case of cognitive dissonance with many of them.
There are liberal theists who claim that one can believe in a non-supernatural form of religion without appreciating that any conception of God is by definition dependent on the supernatural. A non-supernatural deity could not possibly be immortal, omnipotent, omniscient or omnipresent. If there is no supernatural realm, and I find it difficult to understand how any sane and rational person living in a contemporary scientific culture can authentically believe that there is, then there cannot be a God in any meaningful sense. Any form of religion which tries to side step the issue of the supernatural has relegated itself to a secular philosophy and whereas there is nothing wrong with secular philosophies they are not religions.
So is theism any of the following:
1 A belief founded on an unexamined prejudice?
2 An instance of cognitive dissonance?
3 A form of mental illness?
3) Is delusional a mental illness?
I've also heard it likened to Battered Woman Syndrome, (which certainly includes cognitive dissonance). Fear of what will happen when you leave the batterer (or your god) keeps folks in it.
Having been an evangelical Christian, I know any time I started asking questions in my head, I was convinced it was Satan trying to pull me away from god. And just like Battered Woman Syndrome, it is very difficult to convince a Christian that they are being deluded, especially since their circles of friends and communities and churches are also Christian.
I agree with both 1 and 2, and although there might be incidents where 3 is true, by and large I don't think it is.
As far as belief in the supernatural being a source of said dissonance, I tend to disagree (except for perhaps in the case of religious scientists). For the rank and file, they don't see any conflict between the supernatural and the world they see around them. In fact, I'd say to them the existence of the supernatural is merely accepted as much as the existence of the computer or phone you are reading this on. When confronted with the lack of evidence, they tend to throw back the "more things on heaven and earth" and the "oh yeah, well my mother's brother's roommate's uncle had a supernatural experience! explain that, smarty!" As I've said before, magical thinking comes naturally to us, critical, scientific thinking does not. It would do well for us to remember that in dealing with most believers: As hard as it may be for us to wrap our brains around from our outside perspective, they really DO believe this shit. And when you get one or a group of them in power, that is when it gets dangerous. I'd rather have a cynical lying hypocrite who just pays lip service to his or her religion in power than an honest true believer: when the rubber hits the road, the hypocrite is gonna do the rational self-preservation thing.
Read "The Last Question" by Issac Asimov if you would like a different take on the question of the supernatural. There is room for many different possibilities.
Here is a link to the story. It's only four pages long.
For me, I had tremendous cognitive dissonance as a Christian. I'd be presented with REAL evidence that threatened my faith, so I chose to not believe the 'real' evidence. Towards the end of my tenure, it was a constant struggle to keep what I knew was real out of my thoughts.
I was also a really cocky arrogant bitch to folks who didn't believe like I did. I was certain I had God on my side, and we were all that way at my church, so it felt like what I had to do, too. It didn't feel quite right to be so bitchy and arrogant to non-evangelicals, but God was on my side. That was awful cognitive dissonance, and I wish I could go back and apologize to people.
When I couldn't find a good answer to a challenge from a non-believer (or a different believer) I just figured someone else must have the answer and I'll learn it in time.
I totally feel you on wanting to apologize to people. I've actually tried to find this one Jewish friend of mine from High School who I tried so hard to convert. In retrospect, I'm glad I failed, but I wish I could find him to apologize for how I treated his faith.