"Still, a flat income tax seems less complicated and more private than a sales tax."
I guess it's a matter of perspective. The FairTax bill is somewhere between 100 - 150 pages and it replaces a system that is more tha 60,000 pages, according to CCH. That 60,000+ page system started out as a flat tax. The leading flat tax bill in the house right now is the Burgess bill, which maintains the current system and adds a flat tax option to it. IOW, it keeps the 60,000 pages and adds a few thousand (or hundred, who knows?). It is hard to sell me on that as a form of simplification.
As for privacy, the federal government does not demand that you report every detail of your finanical life. They don't even receive reports which tie individuals back to tax receipts. They do receive annual reports of earnings, but that is for SS benefit determination. That's pretty hard to get away from.
IT's OK by me that individuals are not tied to tax receipts, but if they aren't how is the quality of income reporting monitored?