I guess it happens more in Asia than other places. I don't believe them myself at first. Even if friends say they've seen them, I always thought that they are just exaggerating and they are just deluding themselves. That is until a recent incident with my friends.
People who can see them actually gather together. That is because they can only share what they can see with each other. Of course, it might be scientific that they might see 'something' because of their psychology or 'brain composition' or something, but sometimes, science cannot explain everything. At least, everything that me, my family and friends have experienced.
Also, if science was everything. Then religion wouldn't exist. Heaven and Hell wouldn't exist, and spirits wouldn't exist. Of course, I believe that there are supernatural beings here, so I don't deny gods and religion. I believe that there are gods as well.
Until Science is able to explain everything, I would think that I'd rather believe in it than not.