Richard Pryor had an explanation in his stand up routine about the inconsistency

White people don't say it nicely

His outlook changed over the course of his career http://www.nytimes.com/2005/12/15/opinion/15iht-edjackson.html?_r=0

"To this day I wish I'd never said the word. I felt its lameness. It was misunderstood by people. They didn't get what I was talking about. Neither did I. ... So I vowed never to say it again."