I'm not so sure I believe in spirits but here are a couple counter arguments:

1) People denied the holocaust while it was happening. Some people still deny the holocaust. Not because it wasn't true but because somethings you just don't want to face. Its horrible, awful and dirties your world view. So you close your eyes and ignore it. Same thing goes for those videos you've seen lately of people dying / injured while other people walk by. To acknowledge means you have to do something about it so it is easier just to not acknowledge.

2) "Everybody" knows that ghosts don't exist. So if you see one and decide to report it, now "everybody" knows you are crazy. Which means a good solid person, even if they can be truthful with themselves, is not going to want to talk about it with other people.

3) Not everybody that reports are fruit loops. That is a gross generalization that wouldn't stand up to any amount of scrutiny.