Rules aside, since they are what they are:
You've made a common mistake here. Dictionaries do not define language, language defines dictionaries, which always lag far behind constantly evolving, contemporary vernacular. If the word "nigger" is commonly used as anything other than an insult, which it is, then dictionaries will change to reflect this; in the same way as they changed when nigger ceased to be considered a neutral term for a Black person.
Far from having only one meaning or use, "nigger" has many. It's been "reclaimed" and is now often heard being used as a term of affection between Blacks, or simply as a replacement for the word "guy" or "person".
"How are you my nigger?"
"What's that nigger up to, he's crazy?"
"You can trust him, that nigger is good"
Even young Whites are beginning to use the term in a friendly way, reference to each other.
http://en.wikipedia.org/wiki/Nigger - this is more up to date than decades old dictionary.
Why then, should "nigger" be punished more harshly than "faggot", when each word has uses outside of being a pejorative term? Are the feelings of LGBT players less important than those of minority ethnic players?