mibs, your post implies that you are in possession of certain knowledge to which no one else is privy, and that's not only a very arrogant claim, it's an impossible one. Reality does indeed impose limitations upon what is possible, but since human beings are not in possession of the total sum of the knowledge of the universe, and since your experience in this instance is non-existent, all you can truthfully say is that you haven't witnessed that which others, because of their experience, know to be reality.
In short, people who claim to have seen ghosts are not necessarily irrational, as you suggest, but your assessment of them as such displays your own failing in your inability to investigate anything that you, yourself, have not witnessed - and that is a limited mind indeed.