Geller was originally a stage magician, doing a perfectly standard act. Everything he does can be replicated, under the same conditions, with stage magic techniques. When conditions are such that stage magic doesn't work, he begs off. When magicians are present, he begs off. Numerous people have caught him cheating, i.e. using stage magic.
Full details are in several books and many magazines.
The bad news is how many people turned out to be that dumb. There is no theoretical reason why these can't exist. Most of the world's small life forms haven't been cataloged yet, so a few large ones aren't out of the question. Except for a few expeditions to Loch Ness, the scientific community has pretty well ignored the whole idea. To be a viable species, there have to be at least hundreds of creatures.