An excerpt from Nancy Birdsall's article in Boston Review:
"Subsequent work by many economists has strengthened my conviction that while inequality may be constructive in the rich countries—in the classic sense of motivating individuals to work hard, innovate, and take productive risks—in developing countries it is likely to be destructive. That is especially true in Latin America, where conventional measures of income inequality are high. It also may well apply in other parts of the developing world, where our conventional indicators are not so high but there are plentiful signs of other forms of inequality: injustice, indignity, and lack of equal opportunity.
Distinguishing between constructive and destructive inequality is useful. To clarify the distinction: inequality is constructive when it creates positive incentives at the micro level. Such inequality reflects differences in individuals’ responses to equal opportunities and is consistent with efficient allocation of resources in an economy. In contrast, destructive inequality reflects privileges for the already rich and blocks potential for productive contributions of the less rich."
And much more in the article (via 3quarksdaily).