The whole reason for the corn subsidy is because of the mission of our agriculture department in the 1970's to create access to abundant, cheap food for the poor classes. Obviously its not healthy in the slightest, but it's hard to argue that they achieved their goal. Those below the poverty line do not contribute to the subsidy, and they get access to inexpensive, sorry tasting beef and HFCS based food products.
I'm not 100% sure about your statement on the sugar taxes. It may be that if you're right about them, then they contribute to the issue. But I really believe the corn subsidy is the real reason it is less expensive to use HFCS in America than real sugar.
I doubt verymuch that it is preference for bad meat, but rather a preference for cheap meat. with the corn subsidy, it is cheaper to raise cattle in confinement farms, rather than grass grazing. Remember, that the poor folks who buy the cheapest meat are not the ones paying for the majority of the corn subsidy.