For ghosts sightings to occur, it means that ghosts must be corporeal. However, ghosts are, by the accounts of individuals who believe in ghosts, incorporeal phantasms. So, we have a case of a ghost-sighting being that of a sighting of a corporeal-incorporeal. That is a contradiction.
To avoid the contradiction, we have two options: say that ghosts exists but they cannot ever be sighted, felt, etc.; or, assert that ghosts exist and exist as corporeal beings, not incorporeal phantasms. The first option is actually defensible, but meaningless. The second option means that ghosts are materialized and, more importantly, always remain materialized (unless you are going to give to ghosts the divine power of self-causation...which, then ghosts become gods). If they always remain materialized, then we ought to be able to both track them and trap them. But, nobody in the recorded history of mankind has ever trapped a ghost. Why is it so tough to trap a ghost? Because they can simply walk through walls, locked doors, vanish into thin air, etc. But, doing all of these things reduces to the same thing: they are immaterial and incorporeal. Which, if so, we cannot ever ****ing see them.
And, if we think we see a ghost, either we are hallucinating (which humans, throughout recorded history, have done concerning many things and due to many causes) or we are just too stupid to actually look for and find the true cause of and the true phenomenon that we, in our ignorance, hurry, excitedness, anxiety, etc., thought was a phantom.
Basically, the concept of sightable ghosts is internally contradictory. Amazingly, I am more absolutely certain that ghosts cannot exist than I am about the non-existence of unicorns (not an internally contradictory concept), flying pigs (again, not an internally contradictory concept), leprechauns (once more, not internally contradictory), etc.
This is why the belief in ghosts and the willingness to believe in ghost-sightings is the height of imbecility. Believing in the existence of a supernatural God is more defensible than believing in ghosts. Not surprisingly, you dismiss the belief in god, yet accept the belief in ghosts.