What do you think all those 50 new collection offices (not counting the satellite offices) would be doing? Sitting around twittling their thumbs?
Or NRST will nudge the states into conformity with the FairTax.
From
A National Retail Sales Tax: Consequences for the States
While many desirable macroeconomic consequences would follow from adoption of a national retail sales tax, there would also be serious effects on state and local government finances. Absent the IRS, it would be more difficult to maintain viable income tax systems. And the costs of financing state and local government services would rise sharply. State and local tax bases would be substantially broadened if they conform to the NRST base; nonetheless, higher rates would be necessary to replace existing revenues and to finance costs of paying the federal tax on state and local government service delivery. Together there seems to be little in a national sales tax that states and localities would find palatable.
For the founding fathers, a balance between federal government and state rights was an issue and the Constitution is a result of the compromise reached. I doubt they would have accepted a federal tax system that reached into the states and taxed every single sale of goods and services conducted (with the exception of business to business, of course) whether between individuals, individuals and business, government and business, government and individuals.
While the FairTaxers promise more freedom from government with their scheme, it looks like the NRST puts the federal government smack dab in the middle of the day to day economic life of Americans in an unprecedented way.