philly is stating mental illness comes in many shades that can have a variety of symptoms.
sometimes people with mental illness can experience a psychotic break, meaning they have lost contact with reality. this can be developed over time, and possibly itself only last for a small amount of time. example of this would be the aurora massacre
psychopaths are people who have not lost contact with reality but have no empathy. this is something that cannot change about the person. these types of people are the ones operating as serial killers; an example is jeffery dahmer
we don't call dahmer crazy. we call him sick, depraved, freak... we don't like him at all. remember, since prisoners have their own code, he was killed in prison.
the ones we call "crazy" when we talk about this stuff we're talking about psychotics, people that have lost touch. these people frighten us because we cannot understand them and they cannot understand us. they are the embodiment of postmodernism. there's no rules, and that's why they are so scary.
i do not qualify religion as mental illness. i think religion itself grows out of evolutionary principles that helped our ancestors compete and survive over other types of humanoids and other animals. religion itself came out of many evolutionary pressures that bound us together into a community. this doesn't mean it's based on real things, this means it served a purpose and it means we are genetically disposed into belief. if anything, us unbelievers are the ones who are outside the norm.