Read here, here and here. There are a multitude of good reasons why subsidizing ethanol production and mandating its use is plain craziness. The most important reason though, is the fact that a gallon of ethanol spews more CO2 than a gallon of gas (we should replace all ethanol with oil-based gas that comes from U.S. resources - "drill baby, drill" policies). If the politicians and the EPA really felt CO2 was a harmful pollutant, and would endanger not only humans but the climate also, they would be morally be obligated to immediately kill the subsidies and mandates. Obviously, it's all about money and control, not reducing CO2 emissions.
"Replacing the US gasoline consumption of 138 billion gallons annually with ethanol biofuel — just as the government energy policy wants to do — would add about 138 billion pounds of carbon dioxide annually from renewable ethanol biofuel. This is an additional 69 million tons of carbon dioxide into the air annually. The government energy policy would increase rather than decrease carbon dioxide into the air, just the opposite of what the government climate policy wants to do."