Than "It's cheap". (Worth the whole 20 minutes, IMHO)
Our defense of the status quo in farming has been about economics, and it is a good defense. But like all defensive strategies, the opposition soon develops counter-strategies.
The worst case scenario for American agriculture is a resurgence of world-wide prosperity that enables food consumers to choose arbitrarily. [Update: In the hard light of morning, this statement doesn't make as much sense as I apparently thought yesterday. Increased prosperity would bring millions of new protein consumers to the market, for one thing. I have no idea what losing high-end consumers would mean, but likely the ratio is small comparing to new middle-class consumers.]
For extra credit: how would you answer chef Dan Barber?