So the English teacher nerd needs to chime in here about Django.
As someone who's taught Ralph Ellison's Invisible Man and Richard Wright's autobiography Black Boy numerous times, the depiction of "Mandingo fighting" in the movie wasn't at all surprising to me. There's clearly reference in the historical record to slaveholders holding boxing and wrestling matches among slaves (see the work of Frederick Douglass for this), and as I was watching the movie, the "Mandingo fight" reminded me of the "Battle Royal" section in Invisible Man (the black narrator is made to fight other blacks for a college scholarship) or even the section in Black Boy, where Wright and another black man are paid $5 by their white employers to fight each other.
I'm not disagreeing that the Mandingo fight in Django is brutal and problematic, but it's hardly new and it feels to me like it's much in keeping with the spirit of what we know about slaveowners (even if it's not completely factual). And, on a purely cinematic level, it pretty accurately (and succinctly) illustrates two things: 1) Candie's depravity, and 2) the height of the stakes for Schultz and Django. Even considering all this, I suppose the argument can be made that Tarantino is cheaply using the brutality of the American past as a plot device, but to do so would be to level a similar charge at Ellison and, less so, at Wright.
I dunno. I just think Tarantino knows exactly what he's doing – what buttons he's pushing – and there's more on his mind than cheap entertainment, no matter how beholden he is to the movies he loved in his youth.