You need to experience a day in the life of a paranoid schizophrenic. They have little or no contact with people. Due to their inability to interact with normal people, they usually shut themselves off to the world. They were once a cult of one, but thanks to the Internet they've found a community to share their delusions just like any other cult.
The people of Heaven's Gate were "targeted individuals". For various reasons they were predisposed to believe outlandish ideas. Applegate scoured the country looking for the people who eventually killed themselves to fly up to the space ship.
But it can lead to delusion. Our lack of understanding of schizophrenia leads some people to believe it's governmental persecution just as victims of the Plagues led some people to believe it was persecution from God. You can read about the many violent religious reactions and strange cults that the Plague created in The Black Death by Phillip Ziegler.
You seem to think that deception is exclusive to government and religious organizations.