Steven Landsburg writes,

How many grapes were sacrificed by growing that California tomato in a place where there might have been a vineyard? How many morning commutes are increased, and by how much, because that New York greenhouse displaces a conveniently located housing development? What useful tasks could those California workers perform if they weren’t busy growing tomatoes? What about the New York workers? What alternative uses were there for the fertilizers and the farming equipment — or better yet, the resources that went into producing those fertilizers and farming equipment — in each location?

The locavore movement says, in effect, that it knows better than the market the true cost of locally-grown vs. shipped-in produce. In fact, locavores know much less than the market. This is a basic and important point of economics. If I were to make a list of ten things that I hope that my students still understand years after they have taken my course, this would certainly be one of them.