Probably, when we didn't knew better we used all sorts of crazy ideas and sometimes we still do. Crazy people always existed
The question is... how come the ritual of exorcism works? Can we kill bacteria with rituals? I hardly believe so.
Next common sense answer could be the placebo effect, of course, it's a possibility, although the range of applicability is not that vast. E.g. you can't cure an infection with placebo, nor epilepsy etc...
What is difficult to reconcile is what happens with these few people that are admitted to a full rite at the Vatican for example. This is no joke. 98% of the people is simply referred to a doctor or a psychiatrist. It's the remaining 2% that doesn't fit with the usual explanations.
The level of distress these people are in is horrendous, they usually show multiple personality disorder that manifest very violently. The real person inside the body is not to be found. At times they show telepathic abilities and stuff flies around without anyone touching it... aka poltergeists.
The priests that officiate the ritual are often times beaten up or they report sudden sicknesses etc... It's not stuff for the faint of heart, and yes it sounds like folklore or outright made up, and yet there are very well documented cases in which very bizarre things happen.
I am interested in that 2% because it's a fascinating anomaly and something that hardly can be explained away with the usual tools. I think that, together with other well documented phenomena (as telepathy), speaks volumes to how little we know about consciousness.
As regards the "G" word I am completely agnostic, these rites work everywhere, no matter the creed, so it's not a prerogative of Christians. Similar rituals are officiated by Buddhists, Hindus etc... The images and symbols used in these rites seem to speak to a higher level of our consciousness. Call it the collective unconscious (as per Carl Jung's theory), higher self, soul...