There is a substantial body of observations that show that societies that are more unequal are more violent, have more crime, and dramatically less healthy. Sometimes this exhibits itself in small but vivid ways. Sapolsky has an example:
The frequency of “air rage”— a passenger majorly, disruptively, dangerously losing it over something on a flight— has been increasing. Turns out there’s a substantial predictor of it: if the plane has a first-class section, there’s almost a fourfold increase in the odds of a coach passenger having air rage. Force coach passengers to walk through first class when boarding, and you more than double the chances further. Nothing like starting a flight by being reminded of where you fit into the class hierarchy. And completing the parallel with violent crime, when air rage is boosted in coach by reminders of inequality, the result is not a crazed coach passenger sprinting into first class to shout Marxist slogans. It’s the guy being awful to the old woman sitting next to him, or to the flight attendant.*
Sapolsky, Robert M.. Behave: The Biology of Humans at Our Best and Worst (pp. 379-380). Penguin Publishing Group. Kindle Edition.