> You could cut that one without any real harm

The risk is going back to the time where we left corn in piles to rot. That's not harmful in any kind of immediate sense, but losing that energy to waste heat instead of converting it back into usable energy is less than ideal.

> and you could definitely cut back on corn

It's not that you try to grow too much corn, but its yield can be pretty unpredictable. Last year, with favourable weather, yields around here were nearly 100 bushels per acre higher than pre-harvest estimates! That is a hell of a lot of extra product that nobody ever expected before the combines started rolling.

And if you plan for those freak years every year, you're going to end up short more often than not. There is a lot of guesswork involved. That is what ethanol was originally intended to be: A way to buffer that guesswork.

> in general and promote some other stuff

Like what?

1. The consumer dictates what you grow. The consumer loves corn (mostly because it turns into meat). You'd have to compel the consumer to eat something else, and that is going to be one hell of an uphill battle. Many organizations have been trying to get people away from meat for decades and meat consumption is only going up. Meat doesn't necessarily have to come from corn, granted, but other options are more expensive. The consumer isn't going to pay more for meat either.

2. Corn equipment is compatible with other human foods (beans, wheat, etc.) that are also being grown in the crop rotation. If you expect a corn/bean/wheat farmer to start growing carrots in place of corn, good luck. They'd never be able to afford the capital expenditure to add carrot equipment to their lineup.