As far as I'm concerned, you have every right to be horrified by these things. They're some of the worst of human behaviors. But you can't really be surprised in a lot of these cases. Why do I say that?
These positions of trust are, for the most part, Callings. People don't go into these careers for the money, they do it because there's some part of them that needs to do it. Teachers who are devoted to the education of the young, police dedicated to the safety of their fellow man, etc. Unfortunately, voters have largely figured out which jobs attract whose with a Calling, and it's all too tempting to cut their funding. After all, those with a Calling will keep doing the job even if they have to take on a second job to pay their rent, or go on food stamps, or supply work-vital supplies out of their own pocket. Pay them less, smash their unions, pass laws forbidding them from going on strike, it's all good. They won't quit, they have a Calling.
Now, don't get me wrong. I'm not saying that treating your public servants shabbily will turn them into criminals. No, there's a different bit of nasty unintended consequences lurking in the wings. Think about it: just as the voters figure that you can treat certain publicly funded groups shabbily because they have a Calling, so too do people who might be good at those jobs but lack a Calling flee to other fields. To take one example I'm familiar with, consider teachers: the burnout rate among new teachers is appalling, and could be improved a lot simply by making sure they only had to worry about doing their job, not also worry about paying rent or having school supplies for their students. So schools are perennially short of good candidates, even when they can afford to hire anyone at all. And rather than hire someone who will drop out in a couple of years, they try very hard to identify those with the Calling, who will stick it out through all the crap, because their motivations are strong.
But those strong motivations won't always be good ones.
The sadist who becomes a cop or a soldier so he can have legal sanction for his brutality is a cliche older than anyone currently alive. Pedophiles seek out teaching jobs because that's where the kids are. Psychopaths might take a job at a nursing home (where pay ain't all that great, considering it requires medical training) in order to kill people under the cover of natural causes.
If you've driven away all the people who don't have a Calling to the profession by offering insufficient compensation, you may still have all the best and purest people in your hiring pool. But you've increased the percentage of the worst and the vilest simply by removing the merely venal and banal.
I don't know about you, but if I can't have a teacher or a cop or a doctor who's motivated by a true Calling, I'd rather have someone who's just in it for the money than someone who took the job in order to find victims. The guy who's a cop because the pay is good enough to remove the incentive for graft might not be all that reliable when I need help, but neither do I have to worry too much that he's one of Alex's friends from A Clockwork Orange....
So, yeah. When it's a calling and you decide to stop paying people enough to attract the merely greedy, you get the outright evil people who see the job as a way to advance their agenda.