Ethanol production steals precious land to produce inefficient fuel inefficiently (making food more scarce and expensive for the poor).
An increase in the demand for ethanol likely an increase in the demand for, example, corn. Normally, one might associate an increase in demand for corn with an increase in the price for corn. However, if the supply of corn is perfectly elastic, we should expect that price will not rise. This situation is depicted graphically below (click to enlarge).
The idea of the above diagram is as follows: corn is supplied and sold to the highest bidder. If we are to have corn going to both corn feed and to ethanol production, then the prices must be the same--otherwise a corn producer would sell it to the higher bidder--law of one price holds. Therefore, price is set by combined demands and corn supply--price is projected back to individual demands and determines quantity.
This assumption as a long-term assumption is not necessarily absurd. We might add that productivity growth is endogenous and inputs into agricultural production have not risen over the last 60 years, while output has risen 150% (it is 250% of what it was in 1948, for the same inputs). We imagine that not only might land use be easy to scale, so might productivity. Data from the USDA on output, productivity, and inputs are displayed in the figure below (click to enlarge).