The 'problem' with police is the same as with other things. Bad drives out good.
First of all, most police forces are pretty good, with well motivated men in the majority. Even now. But, think on it. The power must really appeal to jerks. You will always have these.
The problem lies with leftist media and politicians who sift through this stuff, looking for an incident they can lie about. Thus, you get your Zimmerman, Wilson, etc. Yet even in a poisoned atmosphere, they were acquitted. The current narrative is that white policemen are using blacks for target practice. It's a huge conspiracy man! It's bullshit.
What it succeeds in doing is driving out the good men from police work, who do not want lives and families destroyed by haters for just doing their job. It also results in bad neighborhoods being abandoned and ignored, because anything like real enforcement will only result in headlines and hate directed at the police and charges against them. There is no incentive for good police to do a good job, so the system drives out good and attracts bad.
I have to admit, police have become worse. We see it because 1. their role has changed to revenue gatherer, and 2. its way easier to give soccer moms and middle aged guys in their kid filled vans tickets. It's much easier pushing around harmless folks than facing hardened criminals. The soccer mom or middle aged dad isn't gonna pull a gun, or start a chase, or put a hit out on you.
If we want good police, we need to honor and respect them, and stop demonizing them.