I agree with all of the things you say, because it's all true.
However, I've witnessed the behaviour of mobs in general and Sunderland I particular. I was at Cardiff, York & Chelsea and know the power that a mob can exert over a few poorly trained stewards and the police. It was yobbish behaviour and through good fortune it didn't result in any great problems.
We knew it was yobbish behaviour but we felt we were justified, because of the poor organisation, and it was slightly funny that we could impose our will on the authorities.
Liverpool fans, in those days, had a dangerous culture of 'mob rule' and that was particularly bad at away games in Europe. Mobbing shops, to steal clothing etc, and gaining illegal entry into grounds was openly boasted about.
Because of that, and other aspects of the day at Hillsborough, it's hard to believe that there wasn't any yobbish behaviour. Whether you class that as hooliganism is open to debate.