Ethanol corn is the same as the corn grown for animal feed. https://iowarfa.org/ethanol-center/ethanol-facts/food-and-fu... It isn't human-grade corn.

Between the ethanol and the animal feed, we are encouraging growing way more corn than is needed for food security.

Nope, that's the cover story. The US subsidizes production, not capacity, which results in lots of excess crop that gets dumped on the market and depresses prices and impoverishes competitors. The ethanol mandates were created partly as a response to the problems that this created. But they are mandates for blending in a certain amount of ethanol, producing artificial demand, and putting us in the ridiculous situation where 40% of corn production goes to ethanol that nobody needs. It's the dumbest thing ever and makes no sense, but is very popular with farm states for obvious reasons.

If we actually wanted to maintain spare production capacity, it would look very different. We'd have to pay to keep land capable of growing food even when not growing any. We'd subsidize the inputs (irrigation, drainage, soil) instead of the outputs. We'd avoid overproduction instead of encouraging it, since it's a form of "inflation" that lowers prices and drives out farmers (other than the ones printing money... er, growing unneeded corn).

If food security were a motivating factor in policy, we would be diversifying away from corn, because drought and aquifer depletion are threatening the ability to continue to grow it.

It's mostly done because Iowa hosts (arguably) the most important primary election for presidential cycles.