Time to invest! :greed:
Buy low, sell high!
I think the biggest problem with police, not just in the USA, but all around the world is that it is not exactly a high profile job. You get people with below average intelligence who are suddenly in a position of power. That often ends badly.
I'm not sure I'd characterize it as "below-average intelligence". My guess is its pretty average. Normal distribution curves are very difficult to skew one way or the other, especially at large population sizes.
More to the point, the problem is that, like most people, police are average. But we hold them to higher standards of stability, restraint, avoidance of bias, ethics, and incorruptibility compared to the average person. That's a failure right there. Because the pay and the job isn't enough to warrant attracting exceptional people as a rule... they're pretty much not that far from bus drivers in that regard.
The worst examples you see are in countries where the police are not paid or underpaid... like South Africa. Corruption is almost impossible to prevent with enough bad apples as a normal portion of the general population.
What's probably most missing is better checks and balances to provide oversight. Rather than pretend there are no bad cops, the system needs to acknowledge that there are bad cops and there need to be reasonable ways of either weeding them out or putting them out of potential harm's way.