The standard counter-argument is that the corn grown for animal feed and for ethanol production is not suited for human consumption.
But that's only partially true. We wouldn't eat it directly -- it could still be turned into masa or sugar or some other processed food and then eaten.
Yeah, we're pretty good at making pretty damn anything "fit for human consumption", including quite a few things that are outright poisonous if consumed unprocessed.
The corn grown that’s not for human consumption is only because it’s earmarked for feed or biofuels. Corn is corn. Where I live, 1 in 4 fields is “for human consumption”