Should we replace the income tax with a national sales tax? Some commonsense on the FairTax by the Tax Policy Center:

The tax is designed to protect low-income people from higher taxes via a large new cash transfer program called a “prebate.” Every household would get a cash transfer equal to the amount of tax that a family at the poverty level would owe. (Ironically, this would be the largest welfare program in history.)

The problem is that very high-income households spend only a fraction of their income, while low- and middle-income people spend all or most of what they make.  A sales tax, by design, exempts a large share of income at the top. If it includes a prebate to protect people at the bottom and doesn’t add to the deficit, then it must raise taxes on people in the middle.