Land is land... you grow something else to make ethanol, you are still using land that could be used for food. How is this not obvious to every human being? Do people just lack common sense?
Ok, this may come as a shock but certain crops are suited for different types of lands and environments. Land that wouldn't be suitable to grow something like corn may be suitable to grow something else. Now for the real shocker, certain plants require more water, nutrients (chemicals), and pesticides than do other plants.
So in a nutshell, the grownups are talking about using plants that either readily grow on land that isn't suitable or economically feasible to grow stuff like corn, grow with little or no effort, require substantially less water, require substantially lest fertilizer, require substantially less pesticides, or any combination of the above.
For example, switchgrass (you know, that stuff that grows along highways all by its damned self) from Wiki:
" Switchgrass is both a perennial and self-seeding crop, which means farmers do not have to plant and reseed after annual harvesting. Once established, a switchgrass stand can survive for ten years or longer.[2] Unlike corn, switchgrass can grow on marginal lands and requires relatively modest levels of chemical fertilizers.[2] Overall, it is considered a resource-efficient, low-input crop for producing bioenergy from farmland."
Edit: I know there is also the efficiency of the plant material involved but considering the comment I was replying to I was trying to keep it simple.