It depends how far the "faith" thing goes, just like for people who are considered mentally stable it can be just fine or it can go too far. I knew a number of people with all sorts of mental conditions at a mental health daycare centre, and quite a few of them had faith, for a given value of "faith" - saying grace before eating, believing in going to Heaven after death, attending Church once a week, that sort of thing. You'd not bat an eyelid. But then there were the ones who were sort of "linked" to a specific church, often if they lived nearby. Priests would say things like "you're more than welcome to stop in any time, it's a pleasure to see you," and to a young unemployed man with a lot of time on his hands and a lot of anguish in his head, that's not an offer you turn down. Which led to more than one young man with schizophrenia who I knew (don't know why, but there weren't female schizophrenics there) starting to go to church every day, and then refusing to go anywhere without his Bible, and trying to convert everyone else, and eventually, yes, sitting in the garden fervently explaining to me how people didn't listen to Noah or Moses either, and they turned out to be right, so why shouldn't he be right? Who's to say his "delusions" aren't real, just cos no one else can see or hear them?