Which is, of course, why Tarantino did it. Because if he hadn't, he would look back and see that outside influence/judgment had affected how he made this movie. And in his opinion, the movie is better with that character in it (I agree) -- so he put Jackson's character in. To someone like Tarantino, who really couldn't care less what people think, it's that simple.Samuel L. Jackson plays Stephen’s overblown insouciance and anachronistic mf-bombs to great comedic effect. There are moments, however, when ironies cancel each other out, and we’re left with a stark truth—at its most basic, this is an instance in which a white director holds an obsequious black slave up for ridicule. The use of this character as a comic foil seems essentially disrespectful to the history of slavery.
It also seems that this critic completely ignores the fact that DU is a genre film, and as much an homage to Sergio Leone as it is about slavery (we need only to see his use of dynamite, which was not invented in 1860, and was famously anachronistically used in The Good, the Bad and the Ugly, as evidence of that). The whole Western tradition is one in which two unlikely heroes who need each other team up to defeat some senseless evil, because all the helpless masses are powerless to stop it. Its a superhero aesthetic that Tarantino is very fond of. The fact that Django goes from never holding a gun to shooting the eyes out of a snowman in the space of minutes is an explicit attempt to raise him to the demi-god/superhero plane. Does Superman denigrate police officers? Should we interpret The Dark Knight as an "alternate history"? Is Dr. House an affront to medical doctors? It was an awesome movie, and an awesome story, but not much more. If the audience isn't smart enough to not view it as that, then shame on them.