"Our Constitution was made only for a moral and religious People. It is wholly inadequate to the government of any other." - James Madison

As those were spoken over 200 years ago I think we can forgive the phrasing and understand the meaning of "moral and religious." And though at the time I'm sure these intelligent people thought that morality and religiosity were positively correlated, today I'm almost tempted to say that in my own relationships I see an inverse correlation, and I say that as a deeply religious person.

Plus, police can be more or less corrupt, but you never get 0 corrupt cops. You have always proportion of those who are work with criminals - helping or being direct members. You occasionally even have gangs composed of cops only.