At a Harvard public health conference I attended last month, people striving to find common ground would begin their remarks with statements like "every rational person agrees that cigarette taxes and motorcycle helmet laws are justified." There was much slippery use of the pronoun we, as in "how do we redesign the world so that people exercise more and make good food choices?" To give you a further sense of how isolated I was in worrying about the totalitarian implications of public health, the second most libertarian speaker (next to me) was University of Chicago law professor Cass Sunstein, whose main function was to reassure the attendees that paternalism can be reconciled with libertarianism. Frankly, the conflict between the two was not a major concern at the conference, even though its ostensible focus was "responsibility for health." But Sunstein's examples of how default options can be set to steer people toward what they themselves will ultimately recognize as better choices fit well with the general assumption that social engineering is inevitable and should be aimed at making everyone healthier. I was therefore intrigued by this Wall Street Journal debate between University of Chicago economist Richard Thaler, Sunstein's collaborator on the "libertarian paternalism" concept, and New York University economist Mario Rizzo, who argues that the idea is either meaningless or incoherent. Since the whole thing (unlike most Journal content) is available online free, you can judge for yourself who wins the argument.