Where I am outside of the US, the anti police-corruption police are hated by the normal police, which I think is a pretty good indication of how many police don't like being held accountable. A lot of police misconduct really relates to a culture of closing ranks so it's seen as a betrayal to investigate that properly. It doesn't need to be said that police should be held to a higher standard than anyone else since they gain pretty major privileges and powers, obviously including the legal ability to use deadly force.