Well okay you all think the movie sucks. Yet do you's believe. ?
Exorcism has been around since christanity began. Priests have been doing it for centuries, and still are asked to exorcise to this day. Jesus deciples had the power to chase out demons. So why not God fearing Priests?
Hell is fire and suphur, on record every victim that has claimed to been possess and lived through it have said a strange burning smell of suphur was always present.
Can a person be possessed? I believe so. Medical side of it is they are just crazy/sick etc., But these possessed victims all claim they are not well they know theirs something not right. On the other hand A mad person does not think they are mad but normal like everyone else.