... punishment of non-punishers, a far more dangerous idiom that can lock an equilibrium in place even if it's harmful to everyone involved.

Have you done the math? This would have important implications for the development of intolerant societies - it was clearly crucial to Nazism - but I've never heard of any studies on the subject. People are still working on first-order punishment.

A good reference on that; Simon Gächter, Elke Renner, and Martin Sefton, "The Long-Run Benefits of Punishment", Science 5 December 2008 322: 1510 [DOI: 10.1126/science.1164744] (in Brevia)

Abstract: Experiments have shown that punishment enhances socially beneficial cooperation but that the costs of punishment outweigh the gains from cooperation. This challenges evolutionary models of altruistic cooperation and punishment, which predict that punishment will be beneficial. We compared 10- and 50-period cooperation experiments. With the longer time horizon, punishment is unambiguously beneficial.