The problem is you're making this be an absolute. There is no perfect training for every situation. But there can be better training. Dawgology articulated training thoughts a lot better than I could.

As for the cameras, yes they keep the bad apples in line (not all clearly. That's why we need some reform on other things like qualified immunity. How exactly? That's above my pay grade at this point but i think it would be easier to build that up from scratch than patch the current system.) Remember, a few bad apples spoil the bunch.