You're not taking into account fog [of war, but not war]. Imagine you're walking down the freeway. Nothing I would do and not my preferred form of protest by the way, but it undeniably works. From behind you, you hear screams and might catch a glimpse of people running in a panic before you find yourself running in a panic, not sure where to run so you don't get run over by this semi truck coming at you. You don't have freeway cameras providing you an elevated view, you don't have the benefit of hindsight, you just see a truck entering your crowd of protestors.

You don't know what's happened but it's reasonable to quickly come to a conclusion that the driver may have driving been the truck as a weapon, given some cases in the last decade. If that's so, I think it's also reasonable in the moment to disarm that driver from his weapon.

Some went beyond that and began to beat him out of anger or revenge. That was too far. In the context and emotional charge of the protests and riots, it's not a surprise it happened. For some of them more directly in the path of the truck, surely a fight or flight response was active.

Now with the benefit of video footage and hindsight, obviously the guy should have been left unharmed. The Facebook streamer Justin Goeman was a damn hero in that circumstance for having the presence of mind to do all he could to get the crowd to leave him unharmed. I hope to buy him a beer some day. But if you were on the ground in that crowd, in the fog, in the path of that truck and charged up with anger and frustration, would you have been able to resist the primal reaction? If your peaceful protest was put upon by perceived violence, on a very basic level isn't it natural to return it?

The point of this comment is not to exonerate those who beat the driver but to try to empathize with the crowd's point of view at that moment. I personally did not see malice in his actions, but that was with the benefit of a video taken from an elevated position, and an aggregated description of the event.