

For that to work, you need enough firepower to actually win. Anything short, and it will be a bloodbath, on your side.
By approaching while very obviously not being a threat, it jamms their training, and forces them to think. Once they are thinking, they likely REALLY don’t want to be the ones to start shooting at American protesters.
They are goons, but programmed goons. If you play to the programming then you will get their desired response. By forcing them outside their programming, they have to improvise.
The smarter ones realise shooting first is a bad idea, politically. The stupider ones just want out, and notice the smarter ones seem similarly inclined.
Staying within the programming is a lose-lose situation for the protestors. You need to get outside the patterns to get new results.
It’s also worth noting that this is a very American thing, not a universal one. Your police are very broken, and in desperate need of an overhaul.