I did a little experiment the other day. I stood outside a Whole Foods Market in Washington, DC, with two cartons of large brown eggs. One carton had the words “Non-GMO Project Verified” on it, with a little orange butterfly. It also said cage-free. The other carton had a different label; a green and white circle with the words “USDA Organic.” One other crucial difference: the organic carton cost 50 cents more. I asked shoppers…