FairTaxers like to claim that those engaged in untaxed black market activities will be paying their fair share under their scheme. They also claim that once hidden taxes are removed from products and services, prices will fall roughly equivalent to the amount the FairTax will add (though they're backing off that somewhat). In other words, black marketers would pay about what they are paying now, but those with SS numbers would also get the prebate.
Low income people in the first quintile would actually come out ahead thanks to the miracle of the prebate while those of us in the middle three quintiles would pay more in tax.
The only rational way to reduce taxes, that I can see, is to get spending and the debt under control. That makes no fancy promises, requires work and constant vigilance, but most of us find that real life in the grown-up world is such.