Riley Cooper should not have gotten a punishment at all. He said a word that every black person says to each other. They want to say it is demeaning but they use it like the word "the". Also, this was off the football field. His personal life should not cause any type of punishment in his professional life.
What he said was wrong, but at the same time Black people use the word with each other freely. He was punished for his mistake and I think it was enough based on the severity of the offense. He didn't make a hate speech or anything, he used a word that offends some people (as it should), but people do that every day.