I read Randall Kennedy's book before it was published -- I took his class in Race Relations and the Law when I was in law school (a great class).

The main idea that he stressed to US during the class (and discusses in the book) is that from a historical and legal perspective, the N word is unique, and has never been treated as equivalent to kike or wop or whatever. He documents these legal differences (such as the number of cases where a racial slur inspired someone to violence) and asks why it became so different from other slurs.