If I might take a moment to spare my standard condemnations, a lot of the problem lies not just in selfishness or training but the ethos of these organizations in both culture and goals.
I've seen people point out more than once that modern police surely must be better than, say, the nests of racist corruption or city politics that were more prominent in decades past. This does identify a strange development, because these things while still prominent are definitely less tolerated now, yet paradoxically exist alongside the extreme neurosis and militarization trends that weren't as common during the Y'all Ain't From Here Boy and The Mayor Wants Them Gone period either. (Though Joe Arpaio shows just how far it can still go and that fuckers like him can get away with pretty much any crime short of actual armed insurrection.)
So what the fuck is going on? How can police be less corrupt
and more corrupt?
The answer is in the goals of "policing", as an abstract. The war on drugs isn't solely to blame, but it's certainly the singular largest problem. The whole idea of policing was destroyed by the drug war, twisted out of shape. Drug enforcement is literally the
very first thing a lot of people think about when they think "police". Consider that. That's fucking crazy. If we want to think of police as societal monitors, as people who really are standing against chaotic violence being inflicted on all of us...then what police do now has effectively no relation to that. Nearly all of them are spending nearly all of their time enforcing against what? Drug enforcement and traffic law, and even then tending to target the most benign forms of both?
It should be no wonder to anyone that police casually murder, entrap, and rob people when police have no connection to society and are
encouraged to set themselves apart and above "normal people". They are the "thin blue line". "Civilians" don't understand "what it's like" on the streets we all live on. They "know" when someone is guilty and they have no objection to "hitting people with whatever [they] can" if they feel "disrespected" after hitting a normal person with a life-disrupting charge that most likely is for behavior which is no harm to anybody.
This is a problem deep as human psychology. Police are now encouraged to do no less than dehumanize everybody in society outside of their bubble. That's how in some ways police are becoming even more brutal and even more destructive to society than in the worst pre-modern periods of US history, and why extreme behaviors that wouldn't have been out of place in putting down a civil rights march or clandestinely murdering a "troublemaker" are just suddenly there.
It all comes back to this disconnection. There is no hope for an ethos of public service and discretion in such an environment, and it reinforces itself through even further disconnection by way of training authored by similarly disconnected people and rightfully obtaining the wrath of society through all the horrible shit police do and encourage each other to do. How the fuck are you going to even investigate serious crimes if people have literally come to prefer criminals or are scared to even call the police because of what they might do to them? The only "apples" in the police aren't bad, they're the few people who have the strength of conviction and self-reflection to resist all of the above, and as we've seen even these folk are at risk of targeting by their fellows. The tree is what's rotten.
I'm not nostalgic for the police of an era I didn't live, but I do think police then at least seemed to be a part of society. As they say, your neighbors don't refrain from murdering you because it's illegal, but because of the human pro-social instinct. Modern police are (intentionally, to a degree) taken right out of that system, given extensive legal permissions, and set loose on the world. The results, whatever else they are, should not be unexpected.