Most people don't realize that the FairTax rate is actually the sum of three separate rates, the general revenue rate; the old-age, survivors and disability insurance rate; and the hospital insurance rate. The general revenue rate is set statutorily at 14.91%. The old-age, survivors and disability insurance rate and the hospital insurance rate will change every year (yes, the FairTax rate changes every year) as determined by the Social Security Administration. The charts below show what happens to the general revenue rate when there is an increase in the the old-age, survivors and disability insurance rate and the hospital insurance rate (which are combined here for simplicity).
Example:
Tax Inclusive General Revenue Rate Combined Social Security & Medicare Rates Total Rate
Gross Payment on $1000 item Amount going to General Revenue
(14.91% x $1,298.70)Effective Tax Exclusive General Revenue Rate
Now with an increase in the combined Social Security& Medicare rates (the ones set by the SSA) and keeping the statutory 14.91% general revenue rate.
Tax Inclusive General Revenue Rate Combined Social Security& Medicare Rates Total Rate
Gross Payment on $1000 item Amount going to General Revenue
(14.91% x $1,175.23)Effective Tax Exclusive General Revenue Rate
This shows that if the Social Security and Medicare sales taxes are increased, the gross payment that the general revenue tax inclusive rate is being applied to is increased thereby increasing the amount of tax it collects. So it's a general revenue tax increase, about $50 billion a year, that has never been voted on by Congress or signed into law! None of this would be an issue if the FairTax was stated in the correct tax exclusive method.
There is no one exclusive (no pun intended) way to express tax rates. There is more than one way that may be used each time. The method you choose may or may not be the same I choose.
I choose tax exclusive rates-
under the nrst to determine how much an after tax price will be (eg a $50 shelf price becomes 50*1.3=65)
under the income tax to determine how much I have to earn to be able to pocket a certain amount (eg to save enough to buy that new $50 pair of slacks, I need to earn $65)
I choose tax inclusive rates-
under the nrst to compare to the inclusive income tax rates I pay and to determine what part of my spending goes to taxes
under the income tax to determine what part of my earnings goes to tax
There is no one way more appropriate than another. In fact your assertion, "the reason the inclusive rate is appropriate for the income tax or flat tax, is that a sales tax adds the tax to the base, the income tax or flat tax subtracts the tax from the base." can be viewed differently. "the reason the inclusive rate is appropriate for the nrst, is that a sales tax subtracts the tax from total spent, the income tax or flat tax adds tax to what you must earn to be able to buy something."
6 of one, half a dozen of the other" as grandma used to say.
So while you would like to say that method of rate calculation is a reason for rejecting the nrst, it's not. It's just the reason you're using today to try to dissuade others from embracing reform.