You appear to believe that consciousness is confined to the brain. Is that so?
If so, then your concept of how the brain works and your advice to the mentally ill who hear voices is correct.
But my experience is that consciousness is not confined to the brain. If so, then the voices heard may come from outside the brain, but not necessarily. However, the ones that come outside the brain then have to be evaluated as to their usefulness. Obviously revelation from god or some messenger of god, if that all exists, would be considered useful. The subject then has to decide if it makes sense to pay attention to the advice or whatever they say.
But just as well the voices from the outside may be mischievous or evil. The subject should then not pay attention to them. It's actually quite like this forum. Some of the posts are worthy of engagement and others should be ignored, whether or not this makes them go away.
My experience is that when people who hear voices are convinced that they are real and not produced in their own brain, but that they have the right to pay attention or ignore them, then their illness goes away or is significantly alleviated. I suspect that is the nature of Nash's self-cure.
I have an Asian friend who has the ability to hear the voice of his wife remotely, and vice versa. That is often quite convenient as for example when out buying something he can question his wife about the product or about what he forgot to buy. Of course with the cell phone this ability has been surplanted.
I have another Asian friend, a survivior of the Kmer Rouge, most of whose family was kiled by them, who regularly consults with her dead relatives when making important choices, like buying a used car.
These people are completely sane and hold important jobs, managerial positions, in the USA. They keep their talents to themselves, of course, because they realize they would be discriminated against if society knew about them.
It is rather like Asperger's syndrome. Extraordinary people have talents that more ordinary people like psychologists label as mental sickness. Belief in the paranormal is often labelled as superstition. Extraordinary persons are feared by the ordinary.
Tarvo. You said in another post how ordinary people can influence electronic systems. So you must accept the paranormal as real to some extent. The DUKE experiments indicated that different people had different abilities in this regard with most people having no ability at all. The 5% outcome came from the extraordinary people who had extraordinary success. And those were only the extraordinary ones that passed the mental illness screening. I suspect that the really good ones would attempt to hide their talent. In the old days they would be labelled "witch".