Imagine if the police showed up and started handing out water bottles, rather than assaulting unarmed (but angry) citizens. I think you'd see a different response.
Imagine if the police were trained to remain passive even when struck. A few violent protesters would strike the police, but if they remained passive I don't think it would take the sight of very many passive cops getting beaten up before the crowd would turn on the violent protesters and protect the cops. Seeing someone getting beaten without defending themselves triggers a very powerful gut reaction in people, even when the victim is 'the enemy'.
>Imagine if the police were trained to remain passive even when struck.
Tell me how much it would cost to train a police force to that level of self control, and to be able identify, in a split second, if the person is attempting to do serious harm to you or is just blowing off steam. Once a person is close enough, there are plenty of blind spots to pull a knife out of.
>the crowd would turn on the violent protesters and protect the cops
Crowd psychology overrides individual identity.
https://en.wikipedia.org/wiki/Crowd_psychology
https://twitter.com/TyreeBP/status/1256813343764918272
Granted, the number of people is ~100x different. Still, examples like the tweet above illustrate that the needed 'self control' has existed within about a pay-period or two.