The amiable Joe Stiglitz says that whenever there is a "spillover"—my ugly dress offending your delicate eyes, say—the government should step in. A Federal Bureau of Dresses, rather like the one Saudi Arabia has. In common with Thaler and Krugman and most other economists since 1848, Stiglitz does not know how much his imagined spillovers reduce national income overall, or whether the government is good at preventing the spill. I reckon it's about as good as the Army Corps of Engineers was in Katrina.

Thaler, in short, melds the list of psychological biases with the list of economic imperfections. It is his worthy scientific accomplishment. His conclusion, unsupported by evidence?

It's bad for us to be free.