That is correct. Nearly everyone has an assortment of personal beliefs that are contrary to the available evidence, and they would all be considered delusional if strictly scrutinized.The Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychiatric Association (APA), is the single most important text used by clinicians. It is the diagnostic rulebook. Currently, the DSM grants religious delusions an exemption from classification as a mental illness. The following is the DSM-IV’s definition of delusion:Again, religion gets a pass in society. Why should someone’s belief be a delusion only if it’s held by a minority of people? In the important respect of being “an incorrect inference about external reality that is firmly sustained,” and one that “defies credibility,” religion is a delusion. But note how religious faith is specifically exempted. Further, many individuals’ religious behaviors do indicate a delusional conviction (falling on one’s knees and talking to an imaginary friend, eating wafers, bowing toward Mecca five times a day, and so on).
“A false belief based on incorrect inference about external reality that is firmly sustained despite what almost everyone else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary. The belief is not one ordinarily accepted by other members of the person’s culture or subculture (e.g. it is not an article of religious faith). When a false belief involves a value judgment, it is regarded as a delusion only when the judgment is so extreme as to defy credibility. Delusional conviction occurs on a continuum and can sometimes be inferred from an individual’s behavior. It is often difficult to distinguish between a delusion and an overvalued idea (in which case the individual has an unreasonable belief or idea but does not hold it as firmly as is the case with a delusion)” (2000, p. 765).
Psychologists would be the worst, as the whole profession appeals mainly to people who lack a scientific mindset. So how would they judge what is true or false?
I had an accusation in court that there is a dog that likes to lie in the middle of the street while I drive over in my car, leaving the dog unharmed. I tried to convince psychologist Ken Perlmutter that this was impossible, and was false like most of the other accusations. He did not understand the concept that something like that is impossible. Dogs do not lie still while being run over.
Other shrinks might say, "how do you feel about that?" They are only interested in feelings, not facts.
So you might be considered delusional if you believe in Martians, but not if you believe in Angels.