Social security: fundamentals of privatization

The New York Times > Opinion > Krugman: The Free Lunch Bunch:

There are several ways to explain why this particular lunch isn't free, but the clearest comes from Michael Kinsley, editorial and opinion editor of The Los Angeles Times. He points out that the math of Bush-style privatization works only if you assume both that stocks are a much better investment than government bonds and that somebody out there in the private sector will nonetheless sell those private accounts lots of stocks while buying lots of government bonds.

So privatizers are in effect asserting that politicians are smart - they know that stocks are a much better investment than bonds - while private investors are stupid, and will swap their valuable stocks for much less valuable government bonds. Isn't such an assertion very peculiar coming from people who claim to trust markets?