That's not at all true; except perhaps for extremely historically-grounded drama (which Django is not), drama tends to get less license than comedy.
> but Mel Brooks' style of humor is no longer socially acceptable
Mel Brooks style of humor was never “socially acceptable”, it’s was always transgressive. It's probably not as commercially acceptable in the mainstream film industry as it once was, but that's more because transgressive video entertainment has other outlets and the mainstream film industry is a more mature and more narrowly-focussed industry than it once was.
> We can take issues like race and anti-semitism deadly seriously, but we aren't allowed to laugh about them anymore.
My experience of currently successful (both live and distributed on major video platforms) stand up and other comedy suggests that, yes, we are very much still allowed to laugh at those things. The particular currently successful forms may not look exactly like Blazing Saddles, but while the latter isn't stale, it's also very firmly grounded in the time it was produced (which seems generally true of Brooks’ comedies).