what should have happened, is the conductor should have called the british transport police to be at the next stop. They could have done their job. The conductor didn't care about anyone else on the train he just got irate at the kid. there must be training or company policy which doesn't involve stopping the train until the guy gets off or leaving the train stationary until BTP arrive. So a word from his boss is probably needed. Frustrated or not, he should be able to deal with the situation more effectively than he did.
As for the other people, maybe most of the people in that carriage thought it was wrong for them to man handle someone off a train? maybe the woman sat with her kids right by that guy was worried about the safety of her kids? If i tried to drag someone off a train and someones kid got hurt, i doubt they would turn around and say "good job mate, i wish I could of done that, my kid got hurt but hey ho, you were doing your best to help the rest of us, my 4 year old can take one for the team".
I've only ever used public transport and ive seen bad stuff happen but ive never seen scores of faredogers holding up trains so I don't believe that it's super common. Bendy buses where by FAR worse. I've seen the CRAZIEST stuff happen on bendy buses and nobody bat an eyelid mainly because everyone is terrified. Much worse than a skinny runt sitting on a train.