It goes against economic principles. Basically, trade benefits everyone. The benefit is maximized when each country produces what they are best at producing, even if another country is better than they are. Look up "comparative advantage". Duties, quotas, and subsidies introduce inefficiencies that reduce those benefits because it encourages production of things we aren't good at producing.
Anyway, the duties, quotas, and subsidies, especially on cotton, corn, rice, and sugar, help a small number of U.S. corporations and hurt U.S. consumers and everyone else. If we got rid of duties and subsidies, we could buy food more cheaply and the formerly subsidized corporations could grow something else. Everyone would benefit.