Well then both you and he are throwing out one of the main features of the fair tax. Food water and warmth are the only three things humans must have to survive. Those can normally be paid for completely tax free under the FT. But they aren't free from any cost at all. One must make some income to acquire them. That isn't voluntary. Making income now costs tax money or at least SS/medicare.
The point is, for a large portion of our population they spend every penny they earn and they don't consider any of their spending as discresionary. Almost all of it goes for food, clothing, car, housing, and rent, with a modest amount left over for cable TV, utlities, phones, etc. Most of this spending really falls into the 'involuntary' category unless you think it is reasonable for people to live like the unabomber. From that extreme viewpoint, I guess some of those bills could be considered voluntary. I don't think 99% of people consider those types of expenditures voluntary.
Also, for the truly needy, the ones they claim concern about, there are still the government "safety net" programs which provide all that. With those things provided, the prebate then becomes spending money. Spending money expose itself the the NRST, broadening the tax base.