Unfortunately, biomass ethanol/methanol cannot be the solution to our problems, and these arguments are simply off-base.
Recent arguments about this rely on the energy content of side uses of the corn, as animal feed for instance, which can make corn to ethanol net energy positive - but those side markets don't exist at the vast scale that would be needed to meet US transportation needs.
Pimentel's comment was that even with the best numbers for ethanol production, you would have to convert an area larger than the contiguous 48 states completely over to growing corn, in order to just meet US demand for transportation fuel.
Who does ethanol production help? Zubrin cites farmers in the third world, certainly an interesting idea to everybody who would like to feel good about what they're doing. However, aside from adding a new dependency of the US on those nations with lots of sunny productive land, the history of the international energy business isn't encouraging.
In fact, the argument greatly resembles the whole family farmer argument for legislation that ends up benefiting large corporate farms and food production companies instead. The most obvious beneficiaries with ethanol are the current US primary producers: Archers Daniels Midland. Are their fingerprints on this new push somewhere?