If ghosts really do exist, would you expect them to be dangerous?

So many stories say that ghosts want to kill you or something, but if they really did exist wouldn't they be harmless and sorta just... Float there? Because I keep on going into my room and finding the light off in my closet and the door open. So I keep turning the light on and closing the door, but a few hours later I hear it creaking open. And it has just started to happen around a few days ago. I should just call ghost busters! Lol!