Years ago I knew an Episcopal priest who was commissioned as the exorcist for his diocese. He told me that 95% of the cases that he consulted on were psychological in nature; i.e., to so-called “demonic possession” could be easily explained (and treated) in terms of ordinary mental illness. Of course, that does leave the other 5%! I’m not an exorcist nor a psychologist, so I hesitate to offer what can only be my own subjective speculation, but I will say that I suspect your idea is right — at least 95% of the time, Biblical and other ancient writings about demonic possession probably could be explained in purely naturalistic ways, given our understading of the human psyche. As for that other 5% — is that just the frontier of human knowledge (what we don’t know or can’t explain yet) or perhaps evidence of demonic forces? I’ll trust everyone to form their opinion here!