I definitely understand where you're coming from, but part of the beauty of Tarantino's films is that he tells stories about very harsh realities and ironies of society. Maybe why his usage of the N-word is supposed to leave such a taste in your mouth. He is pointing how how harsh the word is. How people, at one time, used it as just another word when really they were talking about people. Today we hear the N-word used in ways that are less obtrusive, joked about in a 'eh, this word makes me uncomfortable' way, by rappers, and by bigots. What Tarantino points out is that this word used to mean so much more than how we understand it today; he reminds us of its original meaning and how absolutely ridiculous it is that anyone would continue to use the word at all. Which, in a way, is what brought you to your article (which is fantastic, by the way).
As someone who is an ardent fan of Tarantino's, and someone who often gasped 'that is awesome!' during the movie I want to iterate that I wasn't gasping because of the word use, or because some slave is shooting another slave, but because of the background of why Tarantino is having a slave shoot another slave. There is a deep lesson behind his silliness, a dark sarcasm that isn't pointing fingers but instead is a reminder of how far and how little we've progressed as a society.