I don't know. If "suddenly there are ghosts", then either there's a completely natural explanation for why they aren't actually ghosts but just some sort of smo

I don't know. If "suddenly there are ghosts", then either there's a completely natural explanation for why they aren't actually ghosts but just some sort of smoke-show, at which point it's not supernatural but you're back to "realistic violence"... ... or everything you thought about the world is wrong, including physics. Sure, that would make for a good story, and there are stories like that, but that's not what supernatural stories are usually about. The protagonists in those don't usually break down in an existential crisis consuming the rest of the narrative, they accept the supernatural and "deal with the problem at hand". The story is still about the ghost.