You are suggesting that schizophrenia is demonically inspired? I don't believe that. My maternal grandmother was schizophrenic, however she was also an extremely loving and devout Christian; she is the only person I know who accepted faith like breathing. In her later years, before she was diagnosed, her behaviour and attitude became erratic and frightening, but after a brief hospitalization and once she started taking regular medications all those symptoms vanished. There was no change in her religion or her feelings on God, nor did she ever do something like have an exorcism. How can you explain man-made drugs healing something demonic, because it was most definitely healed?
Demon possession is an interesting topic, but I find the idea that demons cause mental illness to be archaic and a bit naive. It seems to be a way for "healthy" (or maybe just undiagnosed) people to distance themselves from mental illness, and to make it seem like those who have mental illnesses are to blame somehow for the problem. I'll admit, mental illnesses can be really scary. I was diagnosed with Borderline Personality Disorder and I'm a cutter, which freaks people out, and I can understand why someone would think that is such a weird problem that it must be inspired by demons or some inhuman force, but it isn't. Most of these illnesses are caused by chemical imbalances, traumas, life events, etc, and are usually cured or at least significantly improved by counselling or medication, or some combination treatment, not involving exorcism.
It's interesting that the new movie coming out, "Emily Rose" something or other, claims to be a true story. Are there any indisputed accounts of possession?