The irony there is that most of the government subsidies and crop insurance programs come with stipulations related to how the crops are used. The last two years corn farmers in my area have had a hell if a time with drought. The corn ends up rotting in the field specifically because they can't claim insurance or get government assistance if they find another use for the corn, even if the other use only pays a fraction of what a full harvest would have yielded.
But mandating a certain percentage of ethanol ensures a minimum level of demand, preventing that problem.