I would rather that my investments grow without the government stealing from my earnings. That is the benefit everyone extolls about retirement accounts (IRA, Roth IRA, 403b, 401k etc. etc.) The problem with a flat tax is that it eats into this growth of capital. Whereas, a constitutionally set consumtion tax on end-products (not a value-added tax that is added at every level of production) would leave investment capital to grow.