The Corn Laws were so divisive in the UK because they were good for legacy nobles who owned vast amounts of rural land but bad for city dewellers and the emerging class of factory owners.
Note the story of
https://en.wikipedia.org/wiki/U.S._Sugar
where particularly
... sugarcane in the United States remains nearly twice as expensive per pound
as in other developed countries due to the failure the industry would face
without government subsidies
In the case of the US our comparative advantage for producing food is large and we don't improve national security by maximizing our production, we just use more fertilizer and get a bigger dead spot where the Mississippi river enters the ocean.
Mass carbs are how you feed people in the kind of emergency that might make having a strong domestic food supply extremely nice. People can always backyard-garden some greens. If you've got enough corn, wheat, rice, and/or potatoes (maybe), the rest will sort itself out. If you're lacking in those, people are gonna die.
You can't run a nation on broccoli and spinach (unless your population consists of Popeye-clones) while you can run it on starchy foods like wheat, corn and potatoes. They may not be the most healthy alternatives but they'll keep you - and your army - alive to live and fight another day. If a nation can not get any broccoli or spinach they'll just get some other green vegetables or do without. If the nation can not get any bulk starch products it is in dire straits. The high status of green vegetables is more of a symptom of overabundance than of their capacity to feed a nation. They certainly make for a healthy addition to a diet but they lack a number of essential things - proteins and fat as well as some vitamins, B-12 being the hardest to find in plant-based foods.
https://en.wikipedia.org/wiki/Corn_Laws
The WTO has been in a stalemate since the Seattle riots of 1999 because developed countries insist on subsidizing and protecting farmers of major crops (the odd thing is that there is little dirigisme for healthy foods like broccoli and spinach but a lot for mass carbohydrates such as corn, sugar,...) but developing countries won't further open any other kind of trade unless the developed world opens up in agriculture.