A good cop is a cop that signs up to enforce the Law and to refuse to carry out their job enforcing the "law." It is a rare occurrence, but they're out there.
Discussion
Every cop makes the choice to enforce an unjust system.
Police are literally just a violent criminal gang given a monopoly on violence by the state.
There is no such thing as a good cop.
They might be a good person who just happens to be really nieve and stupid but they are enforcing evil against humanity.
You just contradicted yourself so I don't see any reason to change my mind.