Why tax income?
How much a person earns is their business, not the governments!
Tax consumption!
Those who earn more, spend more, and will pay their FAIR share!
That sounds good as a soundbite, but when you dig into the "fair tax" details "consumption" includes services.
"Under the FairTax, every person living in the United States pays a sales tax on purchases of new goods and services, excluding necessities due to the prebate. The FairTax rate after necessities is 23%"
That means that everyone who is self employed is going to end up having to collect the 23% tax on the work they provide, and pay it over to the government. In reality the price they can get for their work will be pushed down by some or all of the 23% since customers aren't going to be in a hurry to pay more for the services they buy.
Everyone that is self employed will end up being a tax collector for the government, and filing plenty of paperwork to show that they collected and paid over the right amount of tax. Your statement "How much a person earns is their business, not the governments!" won't apply to everyone who is self employed.
The real risk of the "fair tax" is that we will end up with it and an income tax, because in effect the "fair tax" is already an income tax for service providers.