I dont agree. Racism is a problem but I think corruption is the core. The police are often taught that they are above the law, starting with quotas - which encourage ticketing people for minor, subjective, or fictitious infractions. Moving up to things like parallel construction (lying in court), civil forfeiture (stealing from people), coercing confessions, and more. Then sprinkle in speeding when on duty when there is no reason, or illegally parking at McDonalds to run in for a burger. From small to significant infractions they give themselves and each other a pass, or are taught or encouraged to do wrong. In an environment like that you drop in a couple racists and well...
There are studies on workplace safety. If you want to prevent fatal accidents you start by creating a culture of safety from the bottom. You clean up work spaces. You take care of trip hazards. You measure the number of bandages used each month and take measures to prevent those accidents. Over time this results in fewer fatalities even on large construction projects.
I think the same applies to corruption.
There's a gif that humorously demonstrates this mentality [1] and shows a police officer instinctively pepper spraying the air around him in response to falling down, even though there's no one around him.
Personally, I blame the laws & culture that encourage excessive civilian gun ownership. The common excuse for preemptive police brutality is the fear that a civilian could be reaching for a gun which puts the officer's life in danger. Without guns, police have no excuse to strike preemptively and it'd be much easier to gain political support for de-arming the police.
This is a legislative and judicial issue as well. Politicians, a fair number of whom are former judges, pass terrible legislation that is then prosecuted by DA's with little to no regard for justice (only conviction rates matter, right?), while cases are judged by former DA's who've managed to move up the chain a little. The management layer is a circle of incestuous self aggrandizing bullshit, and while cops are the boots stepping on the people, someone else to managing where, and how most of that stepping happens.