> Maybe not all of them, but enough of them that "police are corrupt" is true.

Usually I would never generalize the actions of a subset to the entire group, but in this case there is a key difference that justifies "(all/most) police are corrupt": the failure to clean their own house of the "bad apples". When a supposedly "good" policeman gives cover and protection to a criminal in their department instead of reporting the crime, they become an accomplice. in many cases, protecting the guilty may even be a crime in itself (misprision of felony[1]).

[1] https://en.wikipedia.org/wiki/Misprision_of_felony#United_St...