Again, something that is just as stupid, if not more, than creationism. but delusion loves company.
I diagree with the Fair Taxers, mainly because IMO we'd end up with both a federal sales tax while keeping the income tax. That's how DC works nowadays.
However, their underlying principles are sound. And there is enough common ground there regarding fiscal conservatism that they can be allies in trying to constrain the Democrats.
But all you can do is call them stupid...