Response to New York City's partial ban on very large sodas has featured a lot of commentary drawing heavily on the "futility" leg of Albert Hirschmann's three-legged stool of the rhetoric of reaction. But if I think back to the evolution of cigarette smoking policy since the late-1980s that you can see the same thing. Relatively few of the measures enacted—a price hike here, a ban on cigarette machines there—seem like public health game-changers on their own terms. But not only is the overall smoking rate steadily falling, but Gallup is out with survey evidence showing that the number of cigarettes smoked by those who do smoke is falling.
We should take that self-reported data with a grain of salt, but the trend seems credible.
I'd speculate that the line of causation has to do with the trend toward banning smoking in bars, which seems to substantially reduce the aggregate quantity of smoking that occurs in them even as people continue to step outside for the occasional butt. That doesn't say anything about the wisdom of what the Bloomberg administration is trying to do here, but I think it underscores the point that public health paternalism works and it works even though it takes the form of incremental measures rather than huge sweeping gestures. If you want to worry about something credible, worry about slippery slope dynamics. No giant sodas in one city and calorie menu labeling on chains nationwide are both very modest gestures, but the same forces that pushed for those will keep coming up with new ways to ratchet up the sigma and inconvenience associated with "empty" calories. For my part, I'm with Ray Fisman and think that taxing sweetened drinks is the promising policy in this regard. Among other things it would also raise revenue, and let us get by with fewer taxes on work and investment.