As others have pointed out - Peter Joseph was difficult to understand. He obviously was well read and had important things to say, but it really just sounded like a jumble of big words and the arguments didn't really make sense. There's likely some sort of framework he's working from that we don't know about. Like if I just walked up to someone on the street and told them that taxes are theft it would be very jarring, maybe even offensive because that statement doesn't fit in with the framework of society that they learned growing up.
For Peter Joseph the ideas of the non-aggression principle probably seems too simplistic compared to the web of thoughts he's woven around his ideal society. To get his idea across he needs to lay the framework in layman's terms and if Stefan had any problems with it they could go through it and talk about it one at a time.