Federalism itself -the provision of both national and state governments – was, and remains, an engine of diversity, creating “circuit breakers” in the form of a variety of sovereigns accountable to separate regions.  In the federal system, social influences may produce error in some states, and states can certainly fall into cascades. But the existence of separate systems creates a check on the diffusion of error. In this respect, federalism permits states to restrain one another. A particularly important part of this process involves the right of individual citizens to exit. If one sate oppresses its citizens, they have the freedom to leave. That very freedom creates a before the fact deterrent to oppressive legislation. It also creates an after-the-fact safeguard. In this sense, the right to travel from one sovereign state to another is first and foremost a political right, akin to the right to vote itself. Competition among the states provides some protection against the movement of unjustified cascades from one state to another. And if a form of group polarization occurs in one state, the federal system ensures that other states might come to different views. Here, too, we can find a safeguard of liberty.

Cass R. Sunstein, Why Societies Need Dissent, p. 154


Justice Louis Brandeis protest against the Court’s veto (under the Fourteenth Amendment’s due process clause), of an Oklahoma law mildly regulating the ice business: ” It is one of the happy incidents of the federal system that a single courageous state may, if its citizens choose, serve as a laboratory, and try novel social and economic experiments without risk to the rest of the country.”

As found in Fred Rodell: Nine Men, p. 228.