There was one theory I happened upon, and for some reason can't find it through google again ( I should have bookmarked it ) that states ( may not be EXACT, but it's damn close ) :Ghosts Don't Exist. They're Aliens. Aliens live here on Earth but were Forced into hiding because of the mindset that started things like The Crusades and Witch Trials. Some Managed to flee peacefully, but they Have to return to their Home Planet because they require the balanced minerals and vitamins found in Earth's many Natural resources.( I rather enjoyed that one. Not really the silliness of it, because I imagine it Can be possible... but I enjoyed looking up to see how many people believe the same idea. I had a hard time finding anything exactly like it, but it's not a rare idea, apparently. )
I've often heard it said, "Be careful what you wish for;" certainly, with the thought processes that you have shared (and as I enjoy reiterating ), that statement has a totally proper meaning.
This reminds me of a couple of books I read a few years ago. I forget at the moment the title of one of them, but the other was Troublesome Things: A History of Fairies and Fairy Stories by Diane Purkiss.
I've mentioned the idea of doing a cleansing to my boss but he is too worried it would be too close to witchcraft even though I showed him a christian based ritual. He doesn't help the situation by talking about it all the time in addition to books he is writing about hell & the devil. I think he likes having them there, even though he is always freaked out when they make themselves known. I am going to do some research on my own to try to figure out at least who they might be.