I've never really been able to think of that approach as "fair" bunnys. First, knock out the extreme. If someone is below the point of being able to provide for themselves they won't pay taxes. Period. Moving on (with a somewhat oversimplified example, but you get the idea)...
Let's say I'm middle class and you are successful beyond your dreams. I make $100,000/year and you make $100 million. I spend 10% of my income ($10K) on food every year. Under your premise you would need to spend $10 million on food or you would be penalized. To take it all the way, what happens if you actually DID spend 10% of your income on food, just like I did. It certainly wouldn't be fair to penalize you then, would it?. What about other (Federal) expenditures? We both drive our cars on the same highways. Why should it cost you $10.00 in taxes for every mile you drive when it only costs me $.10? What about defense? Does the military do more to protect my house than it does yours? Probably not. Even under a flat tax you would be paying exponentially more for all those services than I would. If the flat tax was 15% I would be paying $15,000 per year and you would be paying $15,000,000. Do you think you would be deriving 1,000 time the benefits I would or could it be that you are, in effect, subsidizing the benefits I get? At what point do you guess you would get tired of doing that?
If I had a deer in the headlights emoticon I would insert it here. I absolutely agree that there is a symmetry to make more, pay more, but in terms of absolute dollars, not dollars AND percentage. This country provides a lot of opportunity to its citizens. Those that have the wherewithal to take advantage of it owe something for the opportunity. That is why an approach like a flat tax makes sense. If you want to make $100K or $100M you know that part of it will go toward supporting the opportunity you had for the next guy. And yes, under that plan the more you make, the more you pay. What I can not stomach is the Robin Hood approach of forcibly taking ever larger slices of someone else's pie as they become successful. Fair is to set the slice taken as the same size (percentage) for everyone. If your pie gets bigger so does the slice you hand over, but the approach of trying to make everyone's bite end up the same usually doesn't work out so well.