Recall that for someone "making" $5M per year, the majority of income that high is inevitiably extractive and exploitative and comes from ownership and power, not the output of their actual work. One could argue if they deserve any of it beyond their actual real wages at a fairly evaluated rate, which might cap out at $1M in a democratic society. FDR proposed a 100% marginal tax rate on the highest earners, his opponents argued him down to something in the 90s, spawning the most productive period in US history.
I don't necessarily find it convincing that the benefit from living in society to an individual is capped, but on the other hand, I don't find it convincing that the benefit from some individual to society is capped either.
We may consider perhaps one can only truly earn $1M. But, what if someone has an idea that benefits a billion people to the value of a dollar each? You may not think, for instance, that Facebook in particular qualifies, but the point is, it seems to me possible in principle. Or, what if someone invents something that saves a million lives? You can't put a dollar amount on that, maybe, but surely it's worth more than $1M, because courts put that much value on just one life frequently.
All in all, the existing situation, where taxes are a percentage of what you make kind of makes sense to me. It is consistent with believing that living in society is a multiplier.
