Sorry but that argument falls apart under a NST, especially one that might come to pass under a democRAT administration. Consider: tax on beef burgers: 1000%, tax on soyburgers: 5% Sure, my purchase of the soyburgers would be "voluntary" but only in the federal lexicon meaning of that word. Don't think it would happen? See Inside Politics: A hard-earned lesson. We have an object lesson of how the government, even a Republican administration, would use a transaction-based tax to modify our behavior.
The FairTax is across the board on all goods and services, not item-by-item.