The study ... found once the threshold was reached, further increases in income tended to be associated with reduced life satisfaction and a lower level of well-being. This may be because money is important for meeting basic needs, purchasing conveniences, and maybe even loan repayments, but to a point. After the optimal point of needs is met, people may be driven by desires such as pursuing more material gains and engaging in social comparisons, which could, ironically, lower well-being. (Purdue News, 13 February 2018: Money only buys happiness for a certain amount)The fairness argument is still the most compelling one, of course. But it's good to know that rich people have reason to support a much fairer pay structure too-even if they find it difficult to look beyond their own self-interest!
P.S. My attention was drawn to the Purdue research by an excellent article in today's Globe and Mail on how large houses can also make you less happy. It's by Matthew Hague; I highly recommend it. (https://www.theglobeandmail.com/life/home-and-design/article-smaller-homes-could-make-us-happier/)
*See "Why Plato was Right: Those at the Top Should Be Paid No More than Three or Four Times What We Pay Those at the Bottom " https://donlepan.blogspot.com/2017/06/bringing-end-to-luck-money-why-those-at.html