Since I ever seen that ghost is exist, I believe things like clairvoyant exist too. I ever meet some who claimed to be one, but I never they proven themselves. Not because they're fraud (through it's possible), but because I prefer not to know about my future.

Prediction and prophecy can be helpful or disaster. The disaster example is on Oedipus history. Through it just a story, I think message is good. If the prophet never speak, the tragedy wouldn't happen. The other example is this old, folk story from Chinese. A boy was predicted to be a successful businessman. The parents so happy they spoiled him. After their demise, boy is now a man who still thinking that he will successful someday. He become lazy, waiting for the prophecy to come true. He dead as poor man. In gate of hell and heaven, he complained about his future with God. God said it will come true, if he working hard.

I don't think I need to provide the example the good one, most people know it.