With my version of “fair” you should rework the federal tax code to be as simple as possible. (snipped)

And you've hit the crux of the problem. Everyone has their own version of "fair". There's a whole spectrum, even if we just restrict it to taxation:

(Note well that I don't claim most of these justifications are reasonable, only that a case could be made)

- Poor people have proven that they don't effectively use their money; rich people have proven that they do. So we shouldn't tax the rich at all, because an optimal allocation of resources would dictate that they should be concentrated where they are most effectively used.

- The poor tend to use more government money than the rich, so the poor should pay higher taxes in dollar amount than the rich do.

- Everyone has the right to consume roughly the same amount of government resources, regardless of what they actually use, so "fair" means to charge everyone for their share, i.e. everyone should be taxed the same dollar amount.

- Poor people shouldn't pay as much dollar-wise as the rich, because that's a bit cruel, but they do consume more "free money" from the government, so should pay proportionally more than the rich; to be "fair" we should tax poor people a percentage that is a bit more than the rich.

- "Fair" can only mean that we take a given percentage of everyone's income, and that this percentage is the same for everybody.

- "Fair" should mean that everybody hurts the same, and it hurts a lot more to lose 10% of $1000 than it hurts to lose 10% of $1 million. So we should have an income dependent rate that goes slightly up the more money you make.

- The last entry is right, but income doesn't effectively estimate how much a tax hurts, because the real pain you feel from tax is that relative to your total wealth. Rich people tend to have far more non-income wealth than poor people, so since we can't really measure wealth, we need to tax their income even more aggressively.

- Fuck Bill Gates, Warren Buffett, and the Google guys, they have more money than God anyways, let's just tax the living crap out of the top 5% progressively (i.e. a billionaire still pays more tax than a millionaire) and leave everyone else alone. There's still a small incentive to make more money, and most companies don't grow based on the personal greed of their most wealthy members anyhow, so our economy will still do just fine, thank you.

Unsurprisingly, people's beliefs about fair taxation tend to correlate fairly strongly to where they lie along the income curve. But the point is, there are a lot of different ways to evaluate "fair" in this context, and "flat" is not necessarily the best answer.

FWIW, if you look at tax rate relative to total wealth, the curve is fairly flat, and it turns out that the middle class actually makes out the best - both the poor and the rich get just about equally screwed.

Which is precisely what the tax burden distribution should look like in a democracy, since the majority of people reside in the middle of the Bell curve and apply downward pressure on the wealth-adjusted tax rate there. The only surprise is that the highest 0.01% doesn't get hit harder than they do, since so much of the wealth is there; that's an indication that our democracy is not person-weighted, but at least partially dollar-weighted.