Demonic possession is a real thing.
Absolutely, but how satan and his demons love to make a mockery of the idea. How much the easier to work their evil when their existence is denied.
So many people pride themselves on being rational and therefore disavowing all things not proved by science which is itself highly prejudice to idea of the possibility of the spiritual world. If these people would open their eyes, and not be controlled by what other people say is rational, the spiritual world would be immensely visible to them via their ability to put things together rationally. But like the old saying so astutely says "There are none so blind as those who refuse to see."