For the basis of clarification.
Income tax occurs currently. If I have money I have saved from now, that is post-tax money, and I have paid income tax on it. If fair tax were to be implemented and I go out and spend that money, I am being double taxed on it, no ifs and ands about it.
So while UnfairTax terminates income tax it doesn't do so retroactively and hence doesn't solve this double taxation problem.