I'm pretty skeptical of the "couldn't be made today" tropes. Some types of films have gone out of style. And there probably are cultural/ethnic stereotypes that would have been mostly considered funny by many audiences that would be more broadly seen as just offensive today.

But I'm not sure how many things are really outright taboo. For example, I've also heard people say that Heathers couldn't be made today--can't be threatening to blow up a school--but it was actually staged as an off-Broadway musical not all that long ago.