This plan hurts the most those people who have saved a lot of money with after-tax dollars.I'm new to this idea, but I don't think it would hurt tax-deferred accounts such as a 401(k)s or Conventional IRAs -- in fact, as I understand it, it would be a boon to holders of such accounts -- but it would hurt non-tax-deferred savings.
I don't think it would "hurt" non-tax-deferred accounts. Their value should hold pretty much the same. However, it will allow any amounts saved in a tax-deferred account to be withdrawn without the taxation intended under our present system.
It took me a little time to wrap my mind around this, but the double tax argument in regards to after-tax savings is not a valid one. As CG & AG point out, the FairTax does add an additional VISIBLE tax, but it also removes the INVISIBLE taxes. It should be close to a wash. It's possible, it will be slightly more, or slightly less, but it should not change very much.
The non-tax-deferred holders were going to be taxed twice on that money under the existing system. The FairTax just makes it more visible. Don't let the visibility confuse you. The tax was there all along under our existing system, just in a different less visible form.