Budiansky does an admirable job informing the debate on local food by criticizing the math of "food miles." Transportation from distant grower to distant market adds very little to the environmental cost of growing food. Home storage and food prep take the lion's share. It is often far more expensive in environmental terms to grow foods out of season in greenhouses than to grow them in season and ship them half way round the world (I can recommend Pretty et al, 2005, and Saunders, Barber, and Taylor, 2006, in this regard. This post compares transportation to heating and cooling).
The Ethicurean does not address any of the substantive points, instead taking issue with the characterization of the local food movement as being dogma-driven instead of acknowledging its important values. The value Eleanor would like us to consider is having a choice. Local food, she claims, is free from massive agroindustrial concentration and so if you want to have any kind of choice about how your food is grown, you have to go local. She thus equates the local food movement with democracy. She argues that also makes food safer (salmonella discussion here and here), though that depends on the education of your local farmer, which may or may not be greater than the corporations' systems and staff.
You don't have to have a local-only system to preserve choice. There are many options: 1 - international competition. Support your highly non-local organic farmer too! 2 - more stringent competition regulation to reduce concentration or apply anti-competitive regs to regions instead of nationally. 3 - mergers among organic (or any other choice you care to favor) producers to produce a large corporation doing something different from the others.
If you care about organic, tell people to buy organic rather than local. If you care about no growth hormones, tell people to find sellers who don't use growth hormones. They may be local. They may not. If you care about supporting smallholder agriculture, support distant smallholders too. At the moment, it probably means buying local, but if organic is important, you save the environment more by buying organic in season from far away than you do buying organic out of season locally. The internet is a wonderful resource for making such connections. That preserves choice without the simplistic "buy local" message that can undermine what some people care about.