It isn’t a large portion of the total corn market, but to take it away or significantly raise its price would have an affect on the food market.
Also, over half the US corn production is used in the US food supply chain.
Reference: http://api.org/aboutoilgas/upload/Energizing_America_Facts.pdf
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My point is that the marketplace, not the government, should dictate how much corn is produced in the US, how the corn is produced and how it is used. While ethanol mandates are wrong, so would be ethanol prohibitions.