None of his rent is taxed now, like it will be under the FairTax.
And if you retain your "tax-free" money under the income tax when you spend it you'll be paying more for whatever you buy due to tax costs embbedded in prices.
Even if you're not aware of it not only does "his rent" have cost components of the current tax system in it but there are also inflated costs due to the tax cost components in things he buys - and in payroll taxes that he sends Uncle. That money has to come from someplace - and it comes from you.