Why are all ghosts depicted as bad?

I was watching Ghostly Encounters on Biography where a man and woman went to this old school. They came across a presence of a ghostly male figure that grabbed the man around the neck and then overpowered the woman with despairing emotions. The show continued focusing on another incident of a young female ghost who left water running and slammed doors and then another ghost story. Every time a ghost was mentioned, they were called a bad ghost.

If you watch movies, read books or other shows abo...