My opinion:
No, we don't need ethanol to off set oil. Proven oil reserves have increased by 50% in the last ten years. Even with increased consumption, oil use will last another 100 years easily. Economics - as the cost of oil production goes up, other alternative energies will become more attractive until oil usage starts to shrink. If the market is allowed to set price, that shouldn't happen for many years.
The biggest problem in the discussion about energy is overcoming the notion that non-renewable fossil fuels are evil. Natural gas should become the first crossover fuel for transportation. It's cheap energy, current engine design is easily changed over to it, and there is already a distribution network. But it's a fossil fuel.
Ethanol is simply not profitable on it's own. The government props up ethanol production, if not by subsidies, than by laws requiring its use. All because a lobby of hand-wringing individuals have convinced the population that renewable fuel is a must or we shall all soon perish.
I don't buy it. I consider the whole problem (along with others) to be created by individuals that always need to have something to crusade against and worry about, to fill a void in their lives. Most likely the void where God should be.
Again, just my opinion.