We don't hold people accountable? Do you really think the police are any better many decades earlier?

For sure, the criminal justice system had gotten worse, with over-incarceration and criminalization, but I doubt that the police are your friends in the 1950s since much of the structure of police organizations hadn't changed that much.

I didn't live in the 1950s but some things that certainly caused where we are today are qualified immunity and powerful unions that are excluded in GOP union busting efforts. States can opt to end qualified immunity for police in their jurisdiction, so it's up to citizens to put pressure on state governments to do so.

https://en.wikipedia.org/wiki/Qualified_immunity

Accountability is exactly what's needed. Police unions, a culture of closing ranks - all this has to go and a top-down change driven by politicians/ministers needs to happen. Chauvin had 18 complaints lodged against him, presumably at least one of those was valid, and so accountability in the form of termination would've avoided what happened. Every private organization would have fired someone with this many customer complaints but the public sector systemically lacks accountability and this leads to terrible outcomes.

>and a top-down change driven by politicians/ministers needs to happen.

I'm not sure if that is politically possible. The police unions start complaining when politicians start to do something (see when they turned their back on DeBlasio in front of news cameras). I'm not sure if it's fixable without repercussions on the offending officers or the union rather than the taxpayers. There is zero or near zero repercussions of the officers, the chain of command or the union for malfeasance. Of course they are going to act how they act, they're humans. The worst part is the bad officers often corrupt the good ones, or make them quit, so over time there's just the bad.