Tarantino's latest film Django Unchained has proven controversial though, not I think for the reasons people are citing. Yes, there's copious use of the 'n-word'. Yes, there's lots of graphic violence. But a serious film can get away with both of these things without anyone batting an eye. Consider the n-word in The Color Purple or the violence of the Normandy Beach scene in Saving Private Ryan. Indeed, Spielburg can even get away with gratuitous nudity as long as its done in a serious, non-sexual way, as in Schindler's List or Amistad, and no one raises a fuss.
No, what really bothers people about Django is that it deals with these things in a film that isn't reverent in its treatment of them, a film that is, in short, fun. It's an extreme form of my father's objection to the (much more reverent) film Life is Beautiful— "I just don't want to see a comedy about the Holocost."
However, I think it's precisely Django's irreverence that makes it so important. Because the audience that goes to see Lincoln or The Color Purple or Beloved or Amistad or pick-your-"serious"-film-about-blacks-in-American-history, is often quite different from the one that goes to see a Tarantino splatter-fest. Indeed, it's easy to argue that people who go see these sorts of films are those most already aware of the injustices being depicted (with, perhaps, the exception of people forced to watch them in school). People who don't like to think about the horrors of slavery, who don't want to think about it, don't go by a ticket to see that kind of movie.
Django on the other hand is much more likely to attract people who merely want a fun rollercoaster of gun battles and desperate heroism. And if Django Unchained were a purely irreverent movie, if it lived in the kind of parrallel fantasy world of say, Wild Wild West, where racism wasn't really a big thing in 19th century America, then the rollercoaster would be all they'd get. But this is Tarantino, so along with all of that flash and thunder, they're forced to confront, to think about, racism and brutality in the slave trade. Further, they will be brought to identify—and root for!—a freed slave battling viscious slavers to rescue his wife.
It's easy to have irreverent movies that never touch on serious issues or serious movies that have no moments of irreverence. But a movie that mixes irreverence and seriousness acheives an effect—an unsettling and powerful effect—and reaches an audience that neither of the other types of movies ever could.
It is the great tragedy of our country that the American experiment was founded on the backs of the slavery of Africans and the genocide of American Indians. And that's why it's important, in a world where people talk about the Founding Fathers as if they were faultless and unquestionable, romanticize the America of the past and veil their racism in a hundred different ways , that we have historical entertainments that, like our history, wade knee deep through a sea of blood.
Further: I haven't touched at all on the ways in which Django is as much a movie about slavery as a movie about representations of slavery in cinema. For more on that see the article at The Film Stage Autobiography, Diegesis and Anachronism in Quentin Tarantino's Dhango Unchained. See also Matt Cheney's brilliant deconstruction of what it means to have historical accuracy and his own argument for why Django is more interesting than Lincoln, Django Unchained and "Accuracy".