To be fair, I am not sure I would call it a 'whim'. The rate is determined by reported wages and reported gross sales tax. The rate changes by numbers collected and calculated by the bureaucrats. The calculation is straight-forward. I just know for myself, my reported wages will go up dramatically under the fairtax. Most of my profits now flow into my income from an S-Corp and with moderate wages. Under the fairtax, there is no reason not to max. out my reported wages to qualify for more benefits. Under the current system I would have to pay an extra 15.3%.
To be fair, I am not sure I would call it a 'whim'.Not the way it's written if you're honest, but then who would stop them from doing it on a whim?