1. It is a primary disorder.
2. It is a stable disorder characterized by the presence of delusions to which the patient clings with extraordinary tenacity.
3. The illness is chronic and frequently lifelong.
4. The delusions are logically constructed and internally consistent.
5. The delusions do not interfere with general logical reasoning (although within the delusional system the logic is perverted) and there is usually no general disturbance of behavior. If disturbed behavior does occur, it is directly related to the delusional beliefs.
6. The individual experiences a heightened sense of self-reference. Events which, to others, are insignificant are of enormous significance to him or her and the social atmosphere surrounding the delusion is highly charged.
The difficulty with the diagnosis of delusions is that almost all of these features can be found in "normal" religious beliefs which hold exactly the same features, yet are not universally considered delusional. For instance, if a person holds a true belief, then they will, of course, persist with it. (Wikipedia)
I have changed my mind about delusions. If we accept the APA definition, it is tempting to conclude that most of the world’s population is mentally ill. Delusions are cultural phenomena that, in the past, were evolutionarily successful because they conferred some benefit on those harbouring the delusions. Humans have invented non-existent supernatural entities, for example, which have helped us to cope with the cruel forces of nature. We have invented gods and rituals in the hope that we could influence them. This is clearly an example of self-delusion.
There are many examples which show that we have inherited many tendencies which do not fit in current society: the urge to kill enemies, to rape, to eliminate competition, and many other tendencies. We must recognize these tendencies and deal with them appropriately. The strong urge to form religions and cults, such as Trumpism, is very difficult to eliminate.
So. I have changed my mind and concluded it is not correct to view religions or cults as a mental illness and that we should seek solutions to human problems by fighting some of the evolved delusions, which were helpful in the past, but are a deterrent in the current society.
Evolution doesn’t stop but, since it is random, we don’t know which direction it will take. Hopefully, the urge to cooperate and having empathy, which were also very successful up to now, will prevail, as the “survival of the fittest” marches on.