Anyone who has studied developmental psychology in recent years has come across the theories of Carol Gilligan. A student of Kohlberg, she challenged the theory of her mentor as she began to see that Kohlberg's stages of moral development value moral positions are more often exhibited by men over those more frequently associated with women. Clearly, Gilligan has hit on a point that is at the heart of all problems of stage theories: given the flexibility of human development and the variety within high functional human behavior, stages often lead to the codification of the researcher's ideas of normal. In Kohlberg's case, he clearly places his judgments about ethics into an understanding of how human beings develop ethically. Another problem is that Kohlberg doesn't address the problem of even defining ethics since philosophy has struggle with this question without any clear resolution. Comparing Kant, Hume, and Levinas, for instance, produces three very different views of what is ethics.
More on ethics to come.