what do you think the vote would be, though? "we don't like him"? last I checked, change.org-petition-style voting didn't have much of an effect on country laws.
It's a duty. Moral, and legal; domestic and international.
Drawing a hard red line at genocide is damn near the very least any human must demand from their leader; perhaps only exceeded by "don't threaten entire civilizations with nuclear weapons".
Same with prosecuting rapist insurrectionists, and going after billionaire's child-trafficking/murdering blackmail rings. These are not "nice to haves" - ya simply gotta do it.
If you're not "mad" when people fail to do these things, then are you really "interested in politics", or are you simply caught in some kind of us-vs-them death spiral?
They learn which crimes are the approved crimes just how an AI machine learning model learns through stochastic gradient descent. They start out committing crimes basically at random, but over time they pick up on the patterns on what crimes are punished (those that are harmful to the system) and which crimes are NOT punished (beneficial to the system), and this causes them all to gravitate towards becoming system enforcers. They themselves aren't aware of their role in the system. They are just blindly following the path of least resistance the state sets up for them, but the state is aware and sets up this reward mechanism to create a system to suppress the citizens that doesn't rely on direct orders that could be traced back to them.
If they were using a secret police force they would slowly lose the trust of the people and begin losing their authority. By using this stochastic citizen suppression model they are able to keep their hands cleaner. People still know they are here and that they are letting them get away with crimes. This arrangement works as long as people think this is good and nobody can make the connection between selective enforcement and an effective police state where criminals are the police.
If the state was caught using secret police to, for example, suppress voters, perform blockbusting, or engage in generally demoralizing behavior they would need to explain themselves. If the state was caught using letting them in and enabling millions of them to suppress the citizenry then you need to explain yourself since you are now a racist bigot.