How do you know it’s inequality when you see it?
There are always unequal outcomes in society, even in the rare cases where there are equal opportunities and equal capabilities. And there are many kinds of inequality. But in modern, monetized economies, income inequality is a good summary measure for all kinds of social inequalities. For good and for bad, money is how we value people and their contributions to society. All monetary economies are unequal, meaning that some people's contributions to society are valued more highly that other people's. They become even more unequal when people save (or to use a less positive word: "hoard") money to pass on to their children to give them an unearned head start in life.
Have levels of inequality gone too far?
For me, that's the relevant question. Inequality is ubiquitous and probably impossible to eradicate, but how much is too much? For example, was 1960s America too unequal, too equal, or "just right"? That's a value judgment that does not have a scientific answer, but as a social scientist I am pretty certain that 1960s America was not so equal that its equality stifled economic innovation (US growth rates were much higher then than they are now) or unfairly penalized hard-working people of high levels of accomplishment (as perhaps professionals unduly suffered during Mao's Cultural Revolution).
