A common reasoning applied to justify disproportional taxation on the income of successful people is that they are "lucky" in the sense that they have talent and drive, whereas other people are "less lucky" and have neither. The "less lucky" ones (less talented, less attracted to hard work) should obviously be compensated, because humanity is a big brotherhood, you see, and everyone should be equal.

This is as opposed to the animal kingdom at large: it would be "silly", you see, to extend the same benefits obtained through coercive taxation to elevate the standard of living for other "less lucky" creatures like gorillas, chimpanzees, or vervet monkeys. The big brotherhood of humanity only extends as far as the human race, you see, it does not extend to an arbitrary number of other creatures that might be even "less lucky", however similar to humans they may be. Besides, we can't subsidize all creatures, where would the limits to that be?

This digression aside, Robin Hanson at Overcoming Bias linked to a New York Times article covering Greg Mankiw's & Matthew Weinzierl's tongue-in-cheek (but seriously analyzed) proposal that, based on the same logic which mandates that successful people should be taxed because of their apparent unfairly acquired talent, tall people should be taxed because on average tall people are paid more than short, simply by virtue of towering over others and thus attracting more confidence:
Should we tax tall workers at a higher rate than their shorter peers? The answer - yes - "follows inexorably" from reigning academic theories of taxation, argues Greg Mankiw. ... Using optimal-taxation formulas, Mankiw and Weinzierl crunch the numbers and come up with a "tall tax" amounting to 7 percent of a tall person's income. Short people would receive a 13 percent rebate.

Do Mankiw and Weinzierl actually endorse such a system? Far from it. Rather, they argue, the proposed tax clarifies our thinking about taxation in general. They say that height is a "justly acquired endowment" ... By the same logic, they imply ... the government has no right to force someone with the "justly acquired endowment" of entrepreneurial genius to pay a higher tax rate.