Last fall, New York Mayor Michael R. Bloomberg asked the U.S. Department of Agriculture to cut soda and other sugar- and corn-sweetened drinks from the list of “foods” that New Yorkers can buy with federal food-stamp benefits. Lobbyists, from soda makers to grocery stores to minority advocates, have fought the proposal. They say that any restriction would represent an attack both on business and on personal freedom for the poor. That argument is flimsy. As food prices rise, and as the federal government cuts back spending, the mayor’s attempt to safeguard the taxpayer dollar is fiscally and socially sound. Back...