If he says he only wants to do it once, he might be telling the truth. Some people just want experiences but don't necessarily have to do them again. However, if he really likes it and wants to do it again, what's the real problem with that?
If he really wants to do it, he will whether or not he has your permission, and I would rather help a friend enjoy his time and make sure he doesn't have a bad trip or do anything stupid by himself.
If I missed your point, it's because I have no idea what you were trying to ask.