There doesn't need to be a reason, if YouTube want's to remove a video from their platform they are free to do so.
But if you're going to ban dangerous/stupid video someone has to make that determination. And you can be sure that there are a ton of activities that are dangerous/stupid in the eyes of some people (even understandably so). BASE jumping, wingsuits, really any kind of extreme sports, stuff with explosives, etc.
People were doing stupid stuff before YouTube existed. As long as it's legal (which this stunt was not) who cares? Teach your son why he shouldn't do that kind of stuff instead of turning to censorship.