Blazing Saddles was a comedy. Django is acceptable because it's a drama, but Mel Brooks' style of humor is no longer socially acceptable. We can take issues like race and anti-semitism deadly seriously, but we aren't allowed to laugh about them anymore.
Which is unfortunate because bigots often take strength from projecting an air of dignity and respectability in an attempt to legitimize themselves in the public square. It's why modern white supremacy and anti-semitism have been reframed as science and philosophy, merely a skeptical form of racial and political realism questioning the mainstream narratives of progressivism and the Enlightment.
Using humor to debase those ideologies and humiliate those who hold them could be a powerful weapon, robbing them of their potency.
Of course, not all such humor has noble intent. The difference between Mel Brooks using racial and religious stereotypes for comic effect and, say, /pol/ doing the same is who the target is, and whether the joke is "punching up" or "punching down." Punching up is funny, punching down isn't. For all of the crass and racial jokes he would make, he, as a white man, still refused to make a joke out of lynching[0].
[0]https://www.youtube.com/watch?v=62cPPSyoQkE