I read the juxtaposition of the "gangsta" personae of Django and Stephen in the pre-Civil War South as an effort to draw a direct link from the "dead" white institution of slavery to the modern day institutionalized slavery vis-a-vis the "gangsta" or "ghetto" culture that has continued to shackle black America. I didn't read it as a conflation of the contemporary stereotype of the black male, but as pointing out the modern day result of slavery.
I think a more explicit blaxploitation version of this revenge story would be to drop two literal modern day "gangstas" into 1860 Mississippi a la Bill & Ted's Excellent Adventure, & have them seek vengeance for slavery that way.
I felt Django - like most of Tarantino's films - gave the vengeance a personal, singular narrative, which for me eroded any potential reading of this film as a 'hood movie for the white people to laugh at. RIGHT below that primary motivation - to avenge what has been done to him & his wife - is the vengeance for the entire institution of slavery, but because that is in actuality a byproduct of the main storyline, I have a hard time reading this film's content as misappropriated.