Do you support the Fair Tax?
Libertarians believe that all taxes are immoral, so none could really be described as "fair."
However, some libertarians support a national sales tax (which is what the so-called Fair Tax is) as a replacement for the income tax. Some of these libertarian Fair Tax advocates feel that people will be much more enraged by a tax that they experience with every purchase, rather than one that is taken from their paycheck before they even see it. With each tax raise, everyone will become acutely aware of how much money is being taken from them. They will hopefully protest, taxes will be lowered, and what we render to Caesar will be lessened.
(Other arguments are also made by some libertarians in defense of the Fair Tax, including claims that it would be less intrusive and less costly than the income tax.)
While the above scenario is a plausible one, I suspect that the Fair Tax will one day be implemented without doing away with the income tax -- thus giving us the worst of both worlds.
I hesitate to support any tax for any reason. Harry Browne and Ron Paul said it best: "Abolish the income tax and replace it with nothing!"