Dude, I don't claim to dispute werewolves, zombies, vampires, trolls, ogres, pixies, fairies, brownies, leprechauns, kappas, sea monsters, sea serpents, Megalodon, Cthulhu, goblins, dwarves, elves or anything of the sort. Hell, I hope to make a living off of them at some point in the future. But I most heartily debunk the idea of coming back after death as some sort of spirit, or further, the idea that there is life after death that you can come back from, at all, ever (in the form of a haunting or whatever). Maybe there's a heaven or a hell, but it's strictly a one-way ticket into either. Here's why.
How many people have died since we could recognizably be called humans? I'm going to go with a nice, round, hundred billion people. That's a hundred billion men, women, children, soldiers, kings, emperors, scientists, peasants, human sacrifices, people of every conceivable size, shape and stripe. So there's some diversity there (just a little, mind you) to pick and choose from.
And if you believe in ghosts, then some of those people (not all, or we'd be up to our collective balls in dead jugglers), more or less arbitrarily, get a second shot at life. Not really life, but the chance to remain on Earth and wander around and be spooky at people.
Now, keeping in mind that every conceivable personality type is also there to choose from, the first thing every ghost ever reported or suspected does upon returning to the land of the living... is skulk around and haunt some random location. Or slink into a corner and make ambiguously creepy noises. I mean, NO ghost gets back to this plane and goes "Hey! I just returned from unspeakable torment in the beyond! I think I'm gonna live a little, go out to some clubs, party down!" No. They go to their randomly chosen location and they STAY there. Forever. That seem a little odd? Doesn't it seem like at least some ghosts would opt to go live the good life?
Also, they tend to be 'seen' in about the least desirable pieces of real estate possible. Shores where ships were wrecked, creaky old houses, caves, graveyards, that whole bit. Wouldn't some ghosts take one look at a dark, dank ossuary and go "Whoa, fuck that. I'm heading for Vegas"?
We're also assuming that all ghosts instantly become morons when they arrive in the real world again. Even assuming there's some ghosts (as is commonly assumed to be the case) that are there to avenge something, or their own deaths, or to find some way to rest in peace, these ghosts apparently feel that the best way to get their point across is... making random noises. Or toppling over a bureau or something to get attention. Hey, if they can make noises, they can talk, and if they can talk they can say "Hey! Current owner of this house! Yes, you, fuckwad! I'm a ghost, my body is in the backyard, go and bury me properly! Thank you, g'bye!" No fuss, no muss, no creepy legends. And even if they can't talk, they can arrange toothpicks or something to say "I AM A GHOST. HEAR ME ROAR." on the table, right?
But the real problem here is awareness of the spirit world. Every single ghost has to have this temptation when they come back to the real world to blow the spirit world wide open, to do shit in a public place that leaves no doubt whatsoever that ghosts are in the house. And you could totally do that. Ghosts with even one of the wide repertoire of skills that are commonly ascribed to them-talking, moving shit around poltergeist-style, possessing people-could do so much shit. They could, say, head over to the White House, yank all the paintings outside and make them dance around on the front lawn. Or possess Barack Obama when he's giving a nationally televised speech and make him do handstands and backflips. Or interrupt an open-air event, steal a microphone and have at the yelling (or float it over the heads of the crowd). The possibilities are literally endless.
And don't mistake how important this would be. If you're a politician, a scientist, a tyrant, a pioneer in your field, people will remember you. But for how long? Who ran against Andrew Jackson for President? My point exactly. What's the name of the guy who discovered continental drift? Yeah, we could look it up, but whoever he is, he ain't a household name. And if you aren't lucky or skilled enough to get yourself into one of those fields, you're kinda screwed as far as remembrance goes beyond your circle of friends, family and coworkers.
The name of the guy that reveals the spirit world to actually exist, the name of the guy or gal who answers one of the most-asked questions in all of history, that name will be remembered forever. Like, for fucking ever. I'm talking Jesus, Moses, Buddha-level ever. Every person on the planet with access to the media will know your name. There'll be religions created about you, there'll be songs, epic poems, books about your life. People will call you a prophet, a saint, a devil, a god. Your name will be in science, in literature, in art, in music, present in every aspect of human life for thousands of damn years. You will have carved your name into history and achieved fame such as few men have dreamed of. You will be the ultimate Internet meme. (Albeit after you're dead.)
And you're telling me that no one, not one single solitary ghost, thinks of this idea and has the ghostly balls and cleverness to pull it off (because if they had, we would know it already). Not one. Ghosts just completely shed human nature once they arrive in the afterlife (which we're assuming they don't because they still have goals that they come back to haunt for, right?). Not one of those kings and emperors, not the greatest minds that ever lived, can figure out what to do and how to do it and get the word to the living that the spirit world exists.
And that is just a crock of shit idea.
So we're left with just two options: Either the spirit world does not exist as something people can come back from, OR Zeus is watching with his thunderbolts and is ready to vaporize every ghost who tries, for whatever reason (maybe he's just bored since Battlestar Galactica went off the air).
So for future reference: if you're in a public place and the lights start to dim, or a chair starts to wobble without anything touching it, or your teacher starts speaking Latin backwards ("Hee mo lay haa") and suddenly everything's back to normal, and then the air smells like ozone... let me know RIGHT THE FUCK AWAY and I will proceed to blow your mind.
I'm done here. Peace out, y'all (and ghosts).