From the economist point of view. The government takes the view that externalities, (things that have either positive or negative effect that goes beyond the price paid for them), must be either taxed or subsidized. If corn is subsidized (ostensibly because it is somehow undervalued), more corn will be produced than consumers really want. As David Friedman's delightful Intermediate Micro-Economic Text reminds us, through a potato metaphor (ironically enough), consumer welfare is ultimately worse off because of the subsidy altered equilibrium. Pollan would tell us that the #2 corn glut has an opportunity cost of less processed foods.
Net result......Consumers Nutrition suffers.
Tom