Granted, about 4/5 of that spending is straight-up welfare for the poor in the form of food stamps, which has nothing to do with farming (and which is undoubtedly a better way of helping people than raising the minimum wage and pushing some low-income earners into unemployment). But that still leaves about $200 billion in welfare for rich farmers—corporate welfare, as it were, because most of it goes to wealthy corporations.
It's clear why these special interests want to keep feeding at the government trough. But why do regular folks want to pay more for things like sugar and dairy products at the grocery store? Why do taxpayers want to subsidize insurance costs for well-to-do agri-businesses? And what do people have against the Florida Everglades, damaged by sugar cane cultivation that wouldn't take place without import restrictions?
Most people probably don't understand the multiple harms of agricultural subsidies. But even if they did, the costs are spread out among the dispersed population, while the benefits are concentrated among the well-connected few who have a strong interest in spending millions of dollars to lobby legislators. Which is a pretty good reason for curbing the power of governments to micromanage the economy. How do we do that? We could start by demanding that all future laws and regulations be simple and straightforward enough to be understood by an educated layperson—and short enough to fit on a single page.