Please correct me if I'm wrong as I don't have that much insight in US law enforcement but I think one of the problems is that local Sheriffs have way too much power. When I see stuff like this
https://en.wikipedia.org/wiki/Joe_Arpaio I'm really glad not to live in the US. There was even a TV series about his deputies and "incompetent fools on a power trip" does hardly begin to describe it. Lack of training might be an issue as well. I know that the Alaska State troopers (whom I would consider rather professional and competent based on what I've seen on TV) only get 14 weeks of training before they are let loose on the public. 14 weeks is in my opinion not enough for teaching the laws, gun skills, martial arts and (very important) deescalation tactics. In Germany police officers get trained between 2.5 and 3 years depending on the career and deescalation is a big part of that from what I hear.
On the other hand there is the problem with most citizens being armed. So the officers always have to assume that someone might pull a gun on them so they probably try to stifle any will for resistance before they can get shot at. That might explain some of the over reactions by some officers. For example searching a house when you think there might be someone with some firearms just waiting for you to open the wardrobe he's hiding in.
