"Saez and Diamond argue that the right marginal tax rate for North Atlantic societies to impose on their richest citizens is 70%.
It is an arresting assertion, given the tax-cut mania that has prevailed in these societies for the past 30 years, but Diamond and Saez’s logic is clear. The superrich command and control so many resources that they are effectively satiated: increasing or decreasing how much wealth they have has no effect on their happiness. So, no matter how large a weight we place on their happiness relative to the happiness of others – whether we regard them as praiseworthy captains of industry who merit their high positions, or as parasitic thieves – we simply cannot do anything to affect it by raising or lowering their tax rates.
The unavoidable implication of this argument is that when we calculate what the tax rate for the superrich will be, we should not consider the effect of changing their tax rate on their happiness, for we know that it is zero. Rather, the key question must be the effect of changing their tax rate on the well-being of the rest of us."