In comparing the two productions, perhaps it should come as no surprise that the film had a much darker, smarter edge to it than the musical, which is actually funnier, campier and more gay than the original. But the fact about the Holocaust is that the Nazis meant business. Sure, decades later there is comfort in not taking them too seriously, in viewing them not with contempt or outrage but with laughter and forgetting. Doing so makes us all feel as if we live in a much safer world. Brooks may have predicted that one day audiences would be unable to distinguish between, or even care about, theater that entertains and theater that offends.
Desensitization is one thing, which is bad enough.
But it's doubtful he ever intended the much darker prophecy of cultural and historical amnesia, as well.