I think Jacques Vallee’s
Passport to Magonia might be onto something. It’s a little more complex than just demons, but also doesn’t exclude the concept.
It’s more like, this is a control mechanism that uses humanity’s curiosity and storytelling functions to keep us off balance. By being mysterious, and a little bit near the edge of our technological conceptions it guides us in a certain direction.
Of course, John Keel at the end of his life also had some insight. That the phenomenon was real, both physical and incorporeal, and feeds off human’s fascination, and energy. And that engaging with it is dangerous and mostly useless. He died a somewhat broken man though.