In a review of Paul Krugman's book Conscience of a Liberal, Herb Gintis says:
... no one cares about inequality. People care about injustice, unfairness, poverty, sexual predators, family values, gay marriage, terrorism, and many other problems of everyday life. People don't care about Gini distributions and other abstractions.
If this is true then there is a lot of irrelevant research on income inequality. Or perhaps,
1) Inequality is correlated with a sense of injustice. When does inequality proxy for injustice or to put it simply, how unequal do income distributions have to get before there is a sense of injustice. Or does inequality as a result of being a robber baron (e.g. corruption) become a proxy for injustice as in some countries.
People hated the Robber Barons because they were robbers and barons, not because they were rich. Oprah Winfrey and Bill Gates do not send the Pinkerton men out to protect their ill-gotten gains; nor to the other super-rich.
2) The statement at the beginning of the blog would then also point to why some results show that inequality is not always correlated with crime and other social problems.
3) What about inequality and financial deepening? There are models that show that inequality is a necessary component of growth in so far as the rich save and invest and hence redirect their wealth toward growth as a whole.