Even rarely means that it has happened though, Draco. And not to say that all law enforcers are crooked and unethical, but it would be more naive for me to believe otherwise.
There are bad people, of course. But not every bad person is the face of a muggle-born or muggle.
The King is just a piece of the puzzle but not the entire puzzle. But what is a King without loyal followers? If the kingdom is divided, it's the Crown's responsibility to smooth things over. Without peace between the two, there is only chaos.