Is income inequality in Boston morally wrong?

Last week, readers of the Boston Globe were treated to yet another article lamenting the fact that Boston, according to an analysis of 2014 Census data by the Brookings Institution, is the U.S. city with the greatest income disparity between the top 5 percent of income earners and the bottom quintile. According to the analysis, the top 5 percent earners in Boston earned $266,000, which was almost 18 times that of the bottom 20 percent.
The question must be asked again, as in an earlier column on this topic: Is income inequality morally wrong? As long as the bottom 20 percent have sufficient means on which to live, why should there be such handwringing over the success of the 5 percent?