Well, you should. Saying "cops are thugs" because some cops are thugs is no different (morally speaking) than saying "black people are criminals" because some black people are criminals. It's wrong to judge an entire diverse group of people by the actions of a few, period.
Cops have the protection of the law and a government granted mandate for violence. They're not a bunch of individuals deciding to act in a particular way. They operate in a system that will protect them for thuggish behaviour. If they happen to be "nice people" as individuals, they still have the option to be a thug without penalty. They still choose to implicitly support wide spread inequality and consequence free violence.
If, as an individual citizen, I'm aware of a serious crime being committed, I have an obligation to report it. If a "good" police officer has knowledge of crimes committed by "bad" police officers and they don't report it, then they are no longer a "good" police officer.
They are categorically thugs. It is literally their job to enforce literally anything with up to lethal violence. It is dressed up in due process and whatnot but it is still thuggery. The difference between, idk cops in France or whatever, and cartel enforcers or a medieval lord's men at arms is mostly one of process, available money and social norms.
A non-criminal black person has no control or responsibility over a random criminal black person.
A police officer absolutely can speak up, speak out, and blow the whistle when one of their fellow officers does awful things. But most will just keep their mouths shut and help (actively or passively) with whatever coverup the institution decides is appropriate.
We're not talking about guilt by association, here. We're talking about guilt by failing to speak up; their silence makes them complicit.
