I remember reports on psychologists using LSD to get into the mindset of schizophrenics and to help treat them... But, it's my understanding that a schizophrenic has difficulty differing between reality and fantasy; they can never turn it off either. They believe what they see because it never goes away, it becomes real to them, they fabricate the fallacies in their head into existance. I wouldn't know for sure though, I've never even met a true schizophrenic.
Here is an example of why I have the philosophy about bad trips that I do: http://www.erowid.org/experiences/exp.php?ID=8371 Hell, that can't even be considered a bad trip with revelations like that. If you FEEL the negative aspects of the human psyche, then you must be able to understand why some people feel the way they do; how can you even consider that to be a terrible experience? Bad trips are a way of understanding things that you previously couldn't, he even decided to quit his drug use because of the trip.