I don't feel that religion is a mental disorder
because people experience life differently. There is nothing wrong with believing in a concept that can't be proved. Columbus believed the world was round before it was fashionable or proved. There are concepts that you can know without proof. For instance, I know for a fact that the sun will rise tomorrow, but I have no proof of that.
The part that is a mental disorder is when you believe that your way is the only way and that others must fit or bend to your ideal of what society and culture should be.
The reason that I consider that attitude a mental disorder is that the people who think that way are denying the fact that there are other people with other valid viewpoints that may differ. It is purposely blinding one's self to the evidence that is all around us. If you don't believe that the world is full of evidence that each person has a unique and valid point of view, then you are very selfish and even cruel, in that you can hurt others by attempting to control their thoughts, feelings, and lives. That, to me, is a disorder.