!! Bit shocked by that. I've never seen the Book of Mormon, and won't be going now.
I guess that the writers, producers and audience felt the humour was OK as it was 'hitting up' at a powerful religious group?? But what's with the attacks on Africans?? (Not familiar with the musical at all, sorry.) And obviously seeing Mormons as de facto powerful and therefore acceptable butts for humour is also problematic.
Just to clarify, with Falsettos, it's not a comedy, primarily, although it has some funny moments within it - the main character dies of AIDS and it is a serious show. The reference to Jewish jokes is rather that it has the same critical look at a community that comedy does, and was originally an 'insider's show' - written, performed and (mainly) watched by largely gay, Jewish, New Yorkers, in New York. So watching it in London, in an audience with (I think) still a high gay quotient, but few Jews (which was obvious when I was one of the only people to 'get' the lines you had to be Jewish to understand) and performed by an entirely non-Jewish cast, was a really uncomfortable experience.
I'm sure it absolutely wasn't intended to be antisemitic, but it was performed by people and watched by people who were outside of the community and seeing it through their eyes meant it ceased to be a community looking wryly at it's own quirks and became others mocking Jewish characters. I don't know what the black equivalent of Four Jews In A Room Bitching would be, but try to imagine a rap song, using the N word liberally throughout, say, sung entirely by white people to an audience of white people. And as part of a musical that ends with the main black character dead. It was just in very poor taste.
There is a long history, by the way, of Jewish roles on the UK stage being played by non-Jews, and usually the Jewish community doesn't complain at all, but in this case, they did. (It went ahead anyway.) I still ended up going to see it, as I'd booked tickets long before they announced the cast, as my dd is a big fan of the musical. But...euggggggh. :(