Argument: Processing cellulose is more difficult than starches
David Schneider. "Loser: Grassoline's Dark Side." IEEE Spectrum. January 2010: "Compared with sugarcane or corn, though, switchgrass is tricky to use, because it provides cellulose—the natural polymer that gives plants their rigidity—rather than simple sugars. So you need to do some elaborate processing, first to break down the cellulose and then to ferment the resulting sugary brew so that it turns into ethanol, which can be served neat or blended with gasoline. As yet, nobody has succeeded in producing switchgrass ethanol on a commercial scale, and the economics of doing so remain fuzzy."