I agree completely, but as a practical matter that is easier said than done. No one has ever claimed psychology is an exact science and how else (other than a criminal background check) do you propose keeping all of those bad apples out of the law enforcement barrel? Many towns can, or choose, to only afford the most cursory psychological evaluation and they probably end up with about the same proportion of good to bad officers as cities with the most elaborate and expensive requirements and testing. If that testing worked the infamous cases of corruption and police brutality that have taken place in LAPD and NYPD could not have occurred.
Frank Serpico contends the corruption in the NYPD he exposed in the early 70s still exists with little real change and that his life is still as at risk in NYC today as it was then. Recent events in the NYPD and the gross disrespect shown by some police officers for the mayor of New York lend credence to Serpico's statements.(...)
To my mind this is where the "but most cops are good!" argument falls down flat. I do believe that genuine bad apples are rare...but that's not the problem. The problem is the
culture promotes harmful ideas and bad behavior, and the social structure of many police offices does nothing to reign in the bad apples.
Bad apples happen in any group of human beings. Doesn't matter if you're talking cops or doctors or Sunday school teachers. You don't protect yourself from the bad apples by trying to screen them out--you can't. That's a fool's errand. You protect yourself from the bad apples by creating resilient cultures of transparency, accountability, and trust.
Police departments in the US seem to have a really hard time doing this. They create structures that, rather than encouraging bad apples to turn good, encourage good apples to turn bad. There is shockingly little accountability and even less transparency. There's an overpowering culture of looking the other way when abuses happen, and of never, ever, ever ratting out a fellow officer, no matter how egregious the misconduct. There's an internal set of ethical mores that prioritizes supporting fellow officers over the well-being of the community they police. In an environment like that, even saints will quickly tend to become corrupt.