This reminds me of the fact that David Hume, the 18th-century Scottish philosopher, thought that underneath the differences among cultures there were certain underlying similarities. He thought that all cultures approve kindness, loyalty, truthfulness, and so on. 

In fairness to Herskovits, however, I think he did allow for the possibility of what he called "universals." These were values or moral views common to all cultures. But, of course, Herskovits didn't just assume that there were universals. He felt that it was an empirical question that could only be answered by careful field work.