“Isn’t ‘revenue neutral’ kind of a moving target?”
Somewhat moving. However, a couple of studies were done in the 2005 timeframe (app.) and they validated the original rate calculations done in the late 90s - within a percentage point or so. The reason is that it is spending that has gotten out of whack, and taxation has not risen proportionately. That is why we have a big deficit. Well, part of the reason. The other is that economic growth has slowed, which is what the FairTax addresses.
However, bear in mind that the revenue neutral calculation is done on a static basis, which is what current congressional rules require. If the calculation were done on a dynamic basis, the FairTax would be highly revenue positive because of the substantial economic expansion it would create.
The dispute over static vs dynamic scoring has, of course, been raging for some time in the halls of congress completely independent of the FairTax.
Then there are those who just want to make sure Washington will still get their money.Revenue neutral, "to make sure Washington will still get their money" . That is the (stated) goal of the Fairtax plan, not mine.