I enjoyed the movie, no problems with it. Understanding the context of the joke, i thought it was funny also.
But i also acknowledge that this lack of sensitivity to racism would only fly when directed towards white people. Every other racial group would have condemned Foxx's comments.
Lets say i was in a cop movie that took place in chicago. I am a "rambo-like cop" that cleans up the streets of chicago with guns blazing and all the exaggerated action shots like Django. After the movie i say
"it sure was fun to kill all those black people"