WHEN market forces cause income inequality to grow, public policy in most countries tends to push in the opposite direction. In the United States, however, we enact tax cuts for the wealthy and cut public services for the needy. Cynics explain this curious inversion by saying that the wealthy have captured the political process in Washington and are exploiting it to their own advantage. This explanation makes sense, however, only if those in power have an extremely naïve understanding of their own interests. A careful reading of the evidence suggests that even the wealthy have been made worse off, on...