The police have taken an oath, have systemic training, and are funded and protected. They should be held to, at minimum, their systemic failures, but probably their oaths and training (which includes constitutional law and appropriate force)

On the other hand, the only thing that protestors have guaranteed to be in common is that they've shown up in a place.

Here's the part you're missing: the protests are holding the police to account, and they're the only way available for the community to enforce basic rule of law on the police. If not for the protests, the officer(s) in question would be getting some paid time off to fund a vacation to the beach. Literally. And that's despite the community already having voted for stricter regulations by clear majorities and not getting them because white votes are counted more in our political system than black ones, and that's despite voter suppression disproportionately restricting black voters' access to the polls.