Some very naive people sign up under the mistaken idea that that is what they will be doing. Those naive people are quickly disabused of this notion, and they either quit, are fired, or join in on the corrupt bastardry. There is no such thing as a good cop. What they do is enforce unjust laws, regardless of what they thought they were going to do.

Keep in mind that if you’ve got 3 bastards in a police department and 17 “good guys” who don’t stop those bastards, you have 20 bastards in that department.