Religion is a Delusion/Mental Illness

[Angrboda]

Religion isn't technically a mental illness, but there is a definite likelihood of it becoming one, when practiced by radical, gullible, close-minded people.

People are suggestible. If the culture you are a part of endorses certain ideas, it's easy for you to endorse them as well. It's a social phenomenon, not a mental illness. This is why "culturally accepted beliefs" are excluded from diagnosis as a mental disorder. I have a history of delusions, being schizoaffective, and religious beliefs are not in the same ballpark. Humans are capable of extreme behaviors under the power of suggestion, that doesn't make them mentally ill. You debase the experience of those with real mental illness and muddy the picture of people without it.

Mental illness diagnoses are designed to group people who might respond to specific treatment together to aid treatment. Religious people are not in need of treatment for mental illness, and so the whole concept of a mental illness diagnosis for them is fundamentally flawed. It's an overreaction to the dissonance between what you believe and they believe. Your beliefs about what is 'rational' don't justify psychologizing people just because you don't share their viewpoint on the rationality of belief, even extreme belief. Extreme beliefs may be unwise, but they aren't per se an illness.