You think that, when told to put down e.g. BLM protests, the cops can just go "nah" and not be fired immediately?

Someone is giving orders, "just" climb the ladder. Also, there is a difference between being there and intentionally (and illegally) target a journalist in the head, for instance.

The orders come from the law, which is that of a bourgeois, white-supremacist state. The fact no cops resisted that kind of behaviour from other cops should be a lesson on the effectiveness of joining the police to change them.