To begin with, the IRS was deemed by The Supreme Court to be unconstitutional. Not just once, but twice. Second, the Constitution does not allow for a tax on personal income -- only on corporate profits... and even those have to be uniform, across the board, for all companies, regardless of size or revenue. Yet, the IRS has created a complex tax code, much longer than the Constitution, but defying it at every turn, creating opportunities for abuse by those who have the means to take advantage of it, and room for error by those who don't... which, by the way, according to the IRS, constitutes criminal charges of fraud and is punishable by imprisonment and theft of assets.
So, in essence, we would be volunteering for a tax that would be Constitutional, thinking that we were lucky because we had eliminated another tax... but that tax is ALREADY illegal!
Even worse, a National Sales Tax could equal anywhere from 18 - 32 %. And that is ON TOP OF any local or state sales tax, any hotel tax, any luxury tax, any "punitive" tax, such as those on cigarettes, and, of course, on top of any gasoline tax.
Not to mention that the Senate and Congress can come back and raise it.