Are police corrupt?
Is the mafia corrupt?
Would the old Chicago mob have been OK if Al Capone* had just cracked down on the corruption in his gang? Or, was the problem more systemic than that? Was the mob functioning exactly as it was intended to?
If your purpose, or at least the real-world manifestation of your "purpose", is evil, how can the word "corrupt" even have any meaning to your situation?
What would a non-corrupt street gang look like? If you eliminate the evil deeds, nothing is left. It is no longer a gang, but is just a non-archating social club.
For police to not be "corrupt" they would have to be funded voluntarily (no "tax" funding at all).
They would have to stop enforcing almost all "laws" and only spend their "on-the-job" time protecting life, liberty, and property.
They would stop enforcing any "law" that forbids you from doing something they are allowed to do (carrying a gun into a post office or school, for example). Yes, this is related to the previous point, but important enough to separate out.
They would have to come down hard on any cop who violated life, liberty, or property, and not form a "blue wall of silence" around him.
They would be accountable for any violations, and would accept the restitution they owe-- personally and individually, not paid to the victims by the "taxpayers".
They wouldn't "patrol", but would only come when invited.
In other words, they wouldn't be cops.
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*Yeah, I realize his mob was less corrupt than today's police, but ignore that for now.