It's Saturday afternoon and you're checking out at your local co-op. You're behind another member of your community, lining up your organic eggs, organic pork chops, organic milk, organic lamb shank, and organic cheese. You feel pretty content. You're eating right, in a world full of chaos. Your body loves you.

And probably best of all, your act of buying organic is part of a political movement; you're supporting a population of small farmers,...