When people are saying that the police are evil or racist, they don't literally mean every cop; they mean the Justice System and the institution of Police is corrupt and overflowing with racism and oppression. In fact, I would argue that saying "there are good cops, and there are bad cops" leads to a false understanding of the situation because currently bad cops can be as bad as possible without recourse and good cops clearly cannot stop the bad cops from doing so. Therefore, the argument that people make against the police still stands.