I apologize, but I don't quite get how you arrived at the conclusion you have, specifically this point. Help me out here?
Here's a good example. Sheriff, under the influence, attempts to interfere with the arrest of a stabbing suspect, buddy of his. https://youtu.be/pKraZkl0-eA
We know about this one sheriff because his staff stood up to him and he got arrested but it tells you a lot about the quality of local law enforcement in small towns.
This isn’t to say that federal policies don’t also have issues. If we think something is a right of all citizens (Such as to not be subject to abuse by the police), that only really takes hold if it is applied across the nation, which is federal.
For example, if I live in a small town that where 80% of the people intent their C code with tabs and I use spaces, they could theoretically elect a police chief who espouses tabs-jingoism and treats spaces-programmers less fairly.
> Leaving it up to local voters makes it sound like it's ok for a police dept to misbehave, eg harass minorities or evade accountability, as long as the majority voters in that city/county are ok with it.
In the extremely unlikely event that a majority are ok with it, yes, that would be correct as far as local laws are concerned. That's what "freedom" means: it means people are free to make mistakes. Note, however, that if the corrupt local cops are violating state or federal law, they're still liable even if a majority of local voters are ok with it. I don't have a problem with, for example, local cops being prosecuted for violating a citizen's Constitutional rights.
However, I strongly doubt that a majority of voters in these localities are actually ok with police corruption. I think they either don't bother voting because they don't think it will make any difference, or don't know about the corruption because they haven't personally experienced the consequences. Even in a large city like, e.g., Chicago, the majority of voters will never have a personal encounter with a city cop.
> going to a couple levels in governance (state or federal) makes total sense given the systematic nature of some of the problems
You're assuming that the state and federal levels of government don't also have systematic problems that would prevent them from fixing corruption. That strikes me as a highly unlikely assumption.
While state and federal government aren't devoid of corruption either, at least more homogeneity can be achieved at these levels. Local jurisdictions are more prone to extreme population disparities just by virtue of being smaller.