I think a lot of people miss the entire point of food subsidies. Like you said, it is about food security. But that is a bit of an abstract concept to a lot of people, a better way to phrase and view it, food subsidies are an alternative to massive granaries storing 1-2 years of an entire nation's food supply. Since food yields naturally vary up to 30% either way, and natural disasters and bad weather can wipe out entire states worth of food, you either need to store all that food as a back up in granaries (which has its own problems), or we can guarantee an overproduction of food so that way if Iowa gets flattened by hail we don't end up with food shortages.