Its about fairness, not equality.
"…there is no evidence that people are bothered by economic inequality itself. Rather, they are bothered by something that is often confounded with inequality: economic unfairness."
This is from a paper published in Nature.
"Drawing upon laboratory studies, cross-cultural research, and experiments with babies and young children, we argue that humans naturally favour fair distributions, not equal ones, and that when fairness and equality clash, people prefer fair inequality over unfair equality."
This is a really short paper, but the examples are pretty amazing. It is a really subtle difference they are trying to highlight, but the implications are huge.
One example has six year-olds distributing erasers to boys who had cleaned up a room. Given an odd number of erasers, they chose to throw out the surplus rather than have an unequal distribution. This obviously leads to the conclusion that equality is important even among children.
But a follow up study found that the children had no qualms about an unequal distribution when they were told that one of the boys had worked harder. This leads to the conclusion that fairness, in fact, is the objective. And it’s backed up by numerous examples, including that we are willing to cop inequality when the cause is chance.
"We suggest that the perception that there is a preference for equality arises through an undue focus on special circumstances, often studied in the laboratory, where inequality and unfairness coincide. In most situations, however, including those involving real world distributions of wealth, people’s concerns about fairness lead them to favour unequal distributions."
It seems that what really triggers us is the process, not the outcomes.
"It follows, then, that if one believes that (a) people in the real world exhibit variation in effort, ability, moral deservingness, and so on, and (b) a fair system takes these considerations into account, then a preference for fairness will dictate that one should prefer unequal outcomes in actual societies."