The real big deal-breaker is that by many metrics, for most accepted processes for fermenting, distilling and distributing corn-alcohol fuel, it takes more energy to make the stuff than you get back when you burn it in vehicle engines. (There's also the little problem that ethanol contains less energy than an equivalent volume...like a gallon...of gasoline, so vehicles not specifically optimized to work most efficiently on alcohol get reduced performance and worse fuel mileage...and there are unfortunate side effects that can damage older vehicles' fuel systems over time.)
I worked with a pilot solar-distillery program back in the early 1980s that could have gone a long way towards turning the balance sheet from red to black. I ran my personal Triumph GT6 on solar-distilled ethanol for some time. There are also better feedstock-plants available for making ethanol that are NOT foodstuffs, grow fast, and are cheaper than corn. But as with most things humans are involved in today, there's FAR more hand wringing, posturing, politicizing, arguing, foot-dragging and finding reasons why NOT to do something than there is just getting down, getting dirty, and making the dammed tech work.
NOTE: Last time I looked, Brazil was doing the best job of getting alcohol fuel from biomass: sugar cane.