The political equality that is required by democracy is always under threat from economic inequality, and the more extreme the economic inequality, the greater the threat to democracy. If democracy is compromised, there is a direct loss of wellbeing because people have good reason to value their ability to participate in political life, and the loss of that ability is instrumental in threatening other harm.

…To worry about these consequences of extreme inequality has nothing to do with being envious of the rich and everything to do with the fear that rapidly growing top incomes are a threat to the wellbeing of everyone else.
Angus Deaton