That's my point.
OK, so what proportion then? I'm guessing the average income of the lowest quartile would be very approximately around the US$20K mark in the US and Europe, considerably less in other parts of the world...so what proportion of $20K would be considered excessive?
It seems that for Europe the factor lies at around 60 and in the US it's around 300. (That are the numbers, off the back of my head, for the difference between the average payment and a CEO salary.)
But that is salary, not income. With a pay-check of $10 million, you'd still have to work 100 years for your first billion.
(So much for some real data points.)
To find an objective point of "excessive" income is impossible (except for fringe cases), as there are no objective criteria. But I think we can establish some intersubjective margins. The objective fringe point, I was referring to above, is when a single entity gets 100% of the GDP. Then that entity would be rightfully taxed at 100%. Also, objective is, that what is average income or below, can't be excessive.
Still leaves a wide margin. We know from experience that the measurable productivity of the top performer vs. the bottom performer in any given group is about a factor of 10. Factor in that some jobs need higher qualification and are inherently more productive, and a factor of 100 seems in the right order of magnitude. (It's also nicely placed between the 60 and 300 for CEO salary.)
That's where I would put the "excessive" mark for income. (And I mean income, not salary. I.e. every $ that shows up in black on your account.)
From these cornerstones, I'd let mathematicians construct a formula for progressive income tax. The limit is 100% at 100% GDP, the turning point (taxes go over 50%) would be at 100 times the average income.
And the point of this discussion (side topic of the current thread and subject of another that seems to have died a natural death) is that "excessive" wealth should be taxed (at 100% mind you)...and (the more on topic discussion) that the only reason we don't all agree to this is because we have all (except apparently a rather small number of exceptionally insightful RF posters) have been "inexplicably" duped by a deliberate program of "capitalist indoctrination" into believing that excessive wealth is a good thing.
So far, as far as I can tell, the only "inexplicable" aspect is what exactly supporters of this 100% excessive wealth tax mean by "excessive" wealth - except that having it is, according to them, "selfish", "greedy" and manipulative to the point of exercising complete control over the entire population.
Note that the above is for
income, not wealth. But I think we could make a similar argument for wealth. But age would have to be a factor, as wealth can be accumulated. I'm against taxing rightfully earned wealth, but I think it would be OK to factor in wealth into the income tax. I.e. if you already have excessive wealth, and still get excessive income, there could be a (low) addition to your income tax.
I'd also be OK with no income tax when the inheritance tax was 100%. It's like paying all your taxes when you're dead and don't need the wealth anyway.