They don't exist, and to prove it I will write out my challenge to any evil (or good) spiritual entities online. When nothing happens, my point will have been proven.
I challenge any supernatural forces or spirits or anything to come prove your existence to me right now. I will worship the first one that appears, so Gods, Goddesses, fairies, Poltergeists, Demons, Devils, Angels, Djinns, whatever, have a race to prove your existence.
Some time later...
I actually feel a bit silly writing this, but nothing has happened. It just goes to show that either A) no conscious supernatural force exists or B) if one exists, it doesn't want us to know about it.