If one believes inequality is a moral wrong, it is one; if one believes it is not a moral wrong, it is not one. That is the nature of beliefs and morality based on beliefs.

John Maynard Keynes anticipated the other half of your thesis. He argued that a strong middle class is necessary for the optimal functioning of capitalism because people in that income range have the money to consume, save, invest, and speculate in proportions that are optimal for the functioning of a capitalistic economic system. So, he said, we should have high marginal tax rates on high incomes and use that money to subsidize the middle class in housing, education, public transportation, and entrepreneurship — which is basically what this country did after WWII with the G.I. Bill of that era.

Extending that model to eliminate poverty proved to be more problematic — in this country, though in Europe they managed it very well. In this country that did and does bring racism into the issue.