Religion is a Delusion/Mental Illness

[Angrboda]

With all due respect, I don't think you know what you're talking about.  Name three diagnoses that fit the pattern you are claiming.

The very definition of "mental illness" ties it to social norms:

A mental disorder, also called a mental illness or psychiatric disorder, is a mental or behavioral pattern or anomaly that causes either suffering or an impaired ability to function in ordinary life (disability), and which is not a developmental or social norm.

http://en.wikipedia.org/wiki/Mental_disorder

"Impaired ability to function in ordinary life" means that one has a problem with dealing with the society in which one lives. 

No it does not mean that.  Impaired function means exactly what it says: an inability to do some or all of the basic tasks associated with work, school, or home life.  It does not mean simply having trouble getting along.  There are people who have trouble dealing with the society they are living in, that does not mean that they are functionally impaired and have a mental illness.  A schizophrenic who can't hold a simple conversation with another person is impaired; not just a person who rubs others the wrong way.

And what will be incompatible with ordinary functioning in a society is largely a matter of the society in which one lives.

No it isn't.  It is largely a matter of what the basic minimum tasks for those life spheres are and whether they can perform them or not.  It isn't at all like what you describe.

As for the claim that religion would be a mental illness if it were not socially accepted, think about someone claiming to have an invisible friend, with magically abilities, who was a guide to the person's life, affecting their social interactions with others, with seemingly arbitrary prohibitions and arbitrary required conduct.  If that were not common and a social norm, it would be fucking crazy.

No, that would be considered unusual, not "fucking crazy."  People aren't diagnosed for being 'different'.  I think you are simply mistaken. I get the impression that you've read about mental illness but don't have much experience with actual clinical practice. Is that accurate?