I think this is a problem online when strong personalities speak, there are always people who go off and hassle the person being talked about. I see that a lot when channels talk about game releases. Often the person making the comments tells the viewers not to hassle.
Another issue I've noticed is the person speaking often doesn't recognise their own influence and power over other people.
The problem is if any of us speak out in a video we're likely to get some people causing trouble. So the question is how much are we liable for the actions of others, and how can we mitigate against it happening, and reduce our liability to speak?
I've no doubt AJ has exploited the situation to mostly make money. But it would have happened to a smaller degree anyway. The situation in principle can happen to anyone with a controversial opinion.
Of course, if he was directly telling people to approach the people involved then it's an open and shut case.