I have done lots over the years with skydivers/basejumpers from helicopters. Some are relatively sane, but the majority - in my experience - are totally irresponsible adrenaline junkies.
Utter ****. I have over 1500 jumps, and I also instruct. Yes, a minority are in it purely for the 'adrenaline junkie' stuff, but to say that is the majority of them are is about as correct as saying 'all helicopter pilots are ego driven homicidal maniacs, with erectile dysfunction issues.'