And the idea that people can just join the police force with good intentions is fatally flawed. The police is a hierarchical organization with a culture that is characterized by its top down command structure. In order to have any influence at all, you have to be at the top...and by the time you get to the top, you're assimilated into the culture. It is self perpetuating.
Absent of firing all the police and starting over from scratch (an option I'm oddly not opposed to), I think the only way we can accomplish this is with strong carrots and even stronger sticks. Taking away qualified immunity is just the first step.
We have laws that punish doctors and lawyers and even commercial truck drivers more harshly when they commit crimes that directly relate to their jobs, under the premise that they know better and should be held to a higher standard. No such laws exist for police, but they should.
I think most importantly though is that we need to protect those who break ranks for good reasons. Retaliation, in any way, shape, or form, by police officers for enforcing the law against another police officer, should be a Class A felony with sentencing in the double digits. And we shouldn't just stop there. Good cops that enforce the law against bad cops deserve our protection, much like how we go out of our way to protect witnesses and whistle-blowers.
And not only that, but there should never be investigations into criminal misconduct by a police officer by other police officers of the same jurisdiction. Once it crosses the line from department policy violation to criminal violation, that investigation should be handed over to a superceding jurisdiction, and any local jurisdiction on the matter should be voided.
I honestly think this might be the only true solution. We have to have police. But right now we have such an entrenched, caustic, tribal, "swamp" of a culture that I don't see how it could possibly be changed without first draining it completely.