For anyone who grew up in the 70s The Exorcist was a cultural force. Not Star Wars level but not far behind. It made people ask “what is an exorcist”. I went to Catholic schools then and a number of nuns swore that exorcisms are real. One nun (circa 1979) told us junior high schoolers how she saw an Exorcism.
Sorry it seems irrational and those “cured” I have to conclude its psychosamatic cure that’s nothing more then a bandaid. It just seems some priests and nuns are just wholly ignorant about mental illness or the patient itself believes they are possessed an exorcism is just part of an overall cure.
I did have a Brother in High School early 80s who absolutely thought the idea of Exorcisms historically stemmed from lack of understanding of mental illness and today’s Exorcisms was just a holdover from that time and field should be done away with.
Its still a scary novel and movie. Both fantastic btw. I may reread the novel I read it in the early 80s in High School, a catholic school.
Also Blatty did a lot more then write the novel he wrote screenplays in the 60s for Blake Edwards also wrote screenplay for Great Train Robbery. He also ghost wrote for Dear Abby a book called Dear Teenager.