The US _has_ been mostly self-sorting for decades now. It&#x27;s one of the reasons politics is so polarized right now and Congress is incapable of governing without a looming emergency.<p>It&#x27;s never as easy as just looking at the outcomes. As with any type of sociology, it&#x27;s not possible to force large sets of people to do identical things for valid control+experimental groups.<p>Methods of taxation, tax rates, size of state government, expectations of government services, natural resources, macroeconomic conditions, talent of the population, and natural economic benefits all distinguish different states. There&#x27;s really no effective way to control for the large variety of conditions across many states.