As with any mention of fair or flat tax, the critics go wild that the poor will be disproportionately penalized with any type of a consumption tax, even one that runs side by side with income taxes. The purchase of consumer items is always going to pain low income folks in the wallet worse than Donald Trump. The price of consumer goods stays the same for everyone, regardless of your income level.
But, let's face it. The money saved in paperwork (tax preparation) and enforcement (i.e. IRS collection efforts to chase down tax debt) goes down. The only problem is that the beast is always hungry and must be fed. I hate slippery slopes, but how long before 9-9-9 becomes 10-10-10 or 33-33-33? Those aren't very catchy numbers for your album (or your portfolio either).