Like Josh said though, some type of irrefutable proof would be helpful.
And that goes for all the things I mentioned above, not just ghosts.
Common sense though, might prevail. My example:
If you were a ghost, what would YOU do? Wouldn't you have some fun? If there are ghosts, why aren't they all doing that stuff all the time?
Why don't you see celebrities on TV talking about ghost experiences (Because wouldn't you surely go haunt one of them for awhile?)
If you were an alien explorer, wouldn't YOU land in a concentrated, populated area or a political site where you could talk to the leaders of that planet? Or would you go land in some backwater bum-**** town and anally probe some in-bred, toothless hick every time you chose to make contact?
Pyschics. If they had all this power to predict things, why wouldn't they use it to gain advantage in their own lives instead of working at 1-900 lines or in some small office in a strip mall?
It's all B.S as far as I'm concerned, until someone reputable can prove otherwise.
Humans have very active imaginations and a desire to make our lives bigger and more epic than they actually are. They tell stories of seeing monsters, ghosts, UFOs and other things so people will pay attention to them...and eventually repeat them so many times with so much embelishment that they actually start to believe it themselves.