I'm not really that surprised. What you're talking about does show up in my world, of course. Though not every death creates a ghost or spirit back home. Most of the time, the soul goes on to their reward. But if they refuse to go with the Reaper when their time is up, they become a ghost. And ghosts often become violent, because they can't really help themselves. Anger is powerful and allows them to affect the world, after all.