But implicit in the argument that local farming is better for the environment than industrial agriculture is an assumption that a “relocalized” food system can be just as efficient as today’s modern farming. That assumption is simply wrong. Today’s high crop yields and low costs reflect gains from specialization and trade, as well as scale and scope economies that would be forsaken under the food system that locavores endorse.Part of the argument is "comparative advantage" and specialization: Iowa gets higher corn yields than Mississippi, Idaho gets higher potato yields than Florida, etc. Part of the argument is "economies of scale".
Makes sense to me, though it's quite possible over the long long term that arguments from evolution will trump the arguments from economies: remember the dinosaurs.