Ethanol is a curious beast in the American political landscape.  It makes bedfellows of ideological enemies, and vice versa.  Consider your comment that conservative lion Rush Limbaugh was supporting his point with commentary cribbed from HuffPo, itself a hotbed of Lefty crazy.  On the other side, you'll likely find typically staunchly-conservative farmers coordinating with green-energy Lefties on pushing a pro-ethanol legislative agenda, the better to support the prices for energy crops.  One more example of how Cash Is King, and why a free market is necessary to ensure a sustaining political and cultural balance.

To answer your question, I'm not sure that any one group is responsible for the anti-ethanol platform.  From the Right, it will tend to be free-market conservatives suspicious of ethanol's prime role in green energy policy from the government.  They also see ethanol as another subsidized boondoggle, pushed initially by ADM to their in-the-pocket politicians.  From the Right's point of view, it's less about ethanol itself, and more about the government sponsorship, and ethanol's place alongside sugar, rubber, etc. as cartel-ized industries.  In essence, the typical Righty exhibits a reflexive disdain for anything that smacks of Big Government.

For the Left, they see ethanol as dangerous to Mother Gaia, requiring ever-more genetically modified corn to feed the Great Ethanol Beast.  You'll also hear Lefties more commonly make the food-for-fuel argument; that uncaring farmers are starving the Third World to feed America's energy addiction.  So, it tends to be more of an environmental Luddite philosophy/irrational fear than anything else.

Truth be told, there are no economically-feasible energy alternatives on the horizon right now.  Ethanol has its drawbacks, but so does wind, hydro, oil, coal, solar, cellulosic, etc. as energy sources.  Perhaps the best possible-yet-unlikely option right now is a national network of nuclear power plants with a commensurate advance in electric cars and their required infrastructure.  That, however, is equally likely to end in political limbo, and/or a failure to develop the required technology without massive government subsidization and regulation.  There's no easy answer, but I'm fairly certain that ethanol has its place more-or-less permanently etched in stone thanks to Bush and Obama's energy plans.