How fair is fair?

Greg Cruey reports that Rudy Giuliani was booed in Daytona over the weekend after he said he would not support a “flat tax.”
Cruey goes on to explain his thoughts and concerns with the “fair tax” and asks, how is the fair tax is really fair?

I’ve always struggled with the definition of the word “fair.” I can’t give you a definition of that term that satisfies me. Most people think of everyone being treated the same.
We don’t treat all kids the same at the school where I work:

• Some of them we make pay for their lunch; others we give lunch to for free.
• Most have to take their math tests in silence and have half an hour; a few, though, get 45 minutes and some help reading the test.
• Some students at my school we make read their books without any sort of devices to help them; others we let wear glasses.

What’s “fair” mean?
I do know this: poor people (and many in the lower half of the middle class) generally spend every penny they get just to make it from month to month. Rich people don’t have that problem. So under the new “fair tax,” a couple in their thirties raising two point four children in the burbs will pay taxes on almost every penny they make just because they spend it while the doctors and lawyers in more affluent neighborhoods, even if they pay more in actually taxes, could get by with paying tax on half or less of their income. Then when you look at the government’s money and you talk about what portion of it came from the wealthy and what part of it came from the average American who’s just try to make ends meet while they raise their kids, you’d find that the “fair tax” reduced the percentage of the Federal budget that was paid for by the more well to do. Rich people will be happy about that.
I’ll ask rhetorically, “how is that fair?” And I expect that someone will explain it to me whether the question is intended to be rhetorical or not…

Thoughts, explanations – I’m interested in an answer as well. Maybe someone from the Mike Huckabee campaign would drop us a note and fill us in. He appears to be the “voice crying out in the desert” when it comes to the fair tax.