Heh. While I am not American, I'd say that 100% of decisions and sovereignty should be at the county or municipality level, with some room for variance here for practical purposes.

With the Dunbar number at 150, adding too many orders of magnitude to that number in population size for a jurisdiction will naturally have negative consequences. We may not know the exact cutoff point where a sound population size turns into a negative in regards to jurisdiction size, but that lack of precise knowledge doesn't change the inherent problems involved.