No...it's not. But the government in their infinite wisdom decided it WAS and incentivized farmers to chase the money and use their crops for ethanol production instead of food production. That led to a full one-quarter of America's corn crop being used for ethanol, which meant there wasn't enough corn left over for food. That led to increased prices on a slew of things that rely on corn (like beef and chicken due to the shortage in corn feed). It drove the price of other crops higher as well because farmers began to plant as much corn as possible, at the expense of soybeans, wheat, and other grains.
But all of those problems cover only the subsidy side of corn ethanol - the functionality of it is what really makes this experiment a historic debacle.
Corn ethanol is 30% less efficient than gasoline and far less efficient than its sugar-based ethanol cousin. Translation: it takes more energy to make corn-based ethanol than other fuels. Not only that, but a University of Minnesota study found that corn ethanol is actually worse for the environment than regular gas. And our genius government to threw $3 billion at it in 2007, an amount that represented 76% of all renewable-energy tax credits.