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.

Your analogy is a false equivalence.