What is not factored into the above is how much is going to be grown anyway. Corn yield in particular can quickly surprise you. Even if you try to only grow enough for food, there will be years where you still have way more than you can handle.

That is why we started producing corn-based ethanol. It wasn't intended to see people grow corn for it, but rather clean up the unmanageable excesses realized in the due course of growing it for food-based reasons that otherwise would have been left out to rot. In that vein, J is insignificant as it is spent either way.

The problem is that humans aren't very good at moderation. A little ethanol production is quite sensible, but once humans get it into their head something might be sensible in small doses they have to take it to a ridiculous extreme... You see that in everything.