In that, you’re wrong, I’m afraid. Since there is no scientific evidence that even one possession has ever occurred, it is not “fallacious to discount” it – until such time as the evidence is actually brought forward.
Only “most cases”? In what cases would you not wait until “last resort”?
If a person’s eyes suddenly started glowing red, they were floating four feet over the bed saying what appeared to be horrible things in a language I knew they had never had an opportunity to hear spoken, I don’t think I’d be starting a major investigation…