Ghosts, If you believe in ghosts, you have simply made anthropomorphic attributions to your optical illusions or hallucinations.
Unexplainable phenomena usually turn out to be caused by pets turning over trash cans, forgetting to do things and thinking you did those things, or doing things and not thinking about them only to find to your surprise that things were done or undone.
Other inexplicable events occur as a result of optical, auditory, or olfactory illusions or hallucinations. When I have free time I'd like to research the boundaries between illusions and hallucinations in the field of vision.
Illusions are created by the limitations and fallibility of our physical perception structure, while hallucinations are the product of incoming stimulus and our cognitive construct whether that be neurological development or conditioning and learning, but usually a combination.
If the authorities can't directly use the threat of "believe or die," they can use junk science and speculation that lends credence to the supernatural.
Faked photographs of ghosts, photographs with optical illusions in them that easily mislead the gullible and videotape of an aircraft or military aerial flairs are some of the culprits that mislead a very large constituency of fools.
As a veteran I've been in combat training exercises and taught to recognize things hurtling through the air, even at night. But, I also learned astronomy growing up, and I had to explain to some of my shipmates standing lookout, that the U.F.O. they thought they were seeing was actually the planet Venus.
On television years later, I saw videotape of aerial flairs that were accidentally launched over a town in Arizona or New Mexico, and the narrator expressing shock and fear, speculating about alien aircraft.
Magic is the best way to keep people somewhat fearful of the world around them, and even more terrified of the unknown.
I keep saying "the authorities," in this case I'm talking about those who are capable of broadcasting deceptive messages to millions of viewers and/or listeners. As long as there are people who insist they had experiences with ghosts, they can still be influenced by religious or spiritual authority of some kind.
People have related to me in the past that they and at least one other witness experienced some sort of ghostly phenomenon. The witness is usually someone who won't disagree, but will play along to maintain a friendship. Or they could be organizations who wish to gather together and profit from hallucinators.
People should be ashamed of themselves for playing along and contributing to the perpetuity of someone's hallucinations. To that end, so too should be ashamed, the Unitarians and the Bahai.