Here is Ed Broadbent, a famous leftist Canadian politician, introducing a talk by Richard Wilkinson given in Canada on income inequality:
I like the bits where he explains that life expectancy isn't correlated well with the average income of a country. But it is well correlated with relative income (social status, social position). This underlines that a society works only if everybody feels like they "belong" and a valued reasonably well compared to others.
I like the quip: "If Americans want to live the American dream, they should move to Denmark or Finland." Those are societies where greater equality means that the offspring of the poor have a better chance to improve their income, status, health, etc. Those societies have greater social mobility.