From Arnold Kling:

Take a look at the top ten countries in the economic freedom index. Then look at the top ten countries by population. The United States is the only country in both lists, and at the rate things are going we will not be in the top ten in terms of economic freedom much longer.

My reading is that there are serious diseconomies of scale in governance. The larger the polity, the worse the ability to govern.

What do the citizens of the state of Massachusetts gain by being a part of the United States? My guess is that the sovereign nation of Massachusetts would greatly outperform the U.S. in policy and economic growth.