hypnosis can definately be a dangerous thing, if not careful with it. i myself have used it in the past, with great effect, for stopping my video game addiction that absorbed all my free time for years.
hypnosis itself, is not a bad thing, its what you use it for. just need to be careful as when you are in a relaxed state, or a state of trance, anything said, can have a lasting effect on your subconcious. and i know from an old friend of mine, can lead to false memories being implanted, of things that never happened.
he was using it to try to recall suppressed memories, and he ended up creating memories of things that never happened. like mmmmm. remembering what things were like at a certain point. noones memories are perfect, and you may end up starting to fill in missing gaps with memories and thaughts that are not real. hypnosis can be very dangerous if you arent careful about what it is you are being hypnotised for. always have a recorder and record any hypnosis sessions, and listen to them at a later point when you arent in a relaxed/trance state to see exactly what the hypnotist said, and what your replies were if your session was of a question/answer nature.