I don't know if you've noticed, but the mainstream is pointing its fat finger and shaking wildly at the Localvore movement. The fact that the a large number of foodies are accepting the Eat Local Challenge and thriving is a source of irritation for a certain type of person. They like to quote studies that somehow show that frozen farmed shrimp from Zimbabwe is somehow more gentle on the planet than buying a local tomato at your farmers market or even foraging your backyard for purslane.
If you are of a certain age, you will remember the beginnings of the feminist movement, which among other things, declared that women really are created equal to men and deserve similar rights across the board. Many, many women who agreed with this basic principal went running the other way. "Oh sure I believe in equal rights for women," they'd declare, "I just don't want to burn my bra or any Women's Lib thing like that." The whole issue was defined by the opposition, who declared that in order to support the feminist cause, a gal needed to burn her bra.
To support the Localvore movement is not to suddenly stop eating catsup from Ohio or even food from China. It's not designed to put foreign imports out of business. It's to encourage local food production, stop suburban sprawl and support traditions that are dying and entrepreneurs who are creating. Take it as far as you can. Don't bust a gut if you have to crack open a jar of imported capers. Think twice before eating the cherries from South America in the winter. Eat more tomatoes when the days are long and more greens and root vegetables in the winter. Get to know a local hunter. Eating rice from another state is not the same things as Fedex'ing a squash blossom across the country. Do your best but don't feel guilty or defensive if you can't get on board with the whole show and don't act smug and superior if somehow you do.
There is just no data that you can offer that will convince me supporting local food is a bad thing.