Sugar is "food".
But we don't want our kids just eating candy.
Corn is sugar.
Show me one child who has died from eating candy, yet we know too much sugar harms health.
But wet corn can develop a poison (aflatoxin), not just a case of sugar.
None of us would feed our children rotten food, which is exactly what aflatoxin corn is, i.e. rotten, molded, poison.
Aflatoxin poisoning usually doesn't kill deer, just makes them less healthy and sometimes very sick. That in turn makes them weaker, and more susceptible to being caught by predators. This is particularly the case with buck fawns. You just never personally see it, but the losses from feeding corn (in a pile or from a feeder) often exceed the benefits. It is a very different situation with a field of corn vs. a pile of corn.
But aflatoxin poisoning is mainly a killer of birds, all birds that eat it. I believe it has been a significant driver of periodic low turkey populations, as well as the near extinction of bobwhite quail. Corn in a pile is candy to birds. When it develops aflatoxin, the birds still eat it (although deer may not). Birds then fly or walk off to die no where near the corn pile, so those pouring out the corn rarely are aware of the dangers of aflatoxin (nor do most seem to even care).