It's not completely insane when you remember that we also grow the crops for food, and exactly matching food requirements with production yield is impossible, so there will be times of gross excesses (especially with corn, which can produce _way_ more than you could have ever dreamed of if the weather is just right). Turning excess product back into usable energy instead leaving it in a pile to rot can be worthwhile.

The problem is that humans don't understand moderation. They heard it makes sense at some small scale and automatically assume it would be even better if we scale it up massively. Now — if you look at the comments here — they heard it doesn't work at massive scale, and take from it that it doesn't ever make sense...