[user104658]

I'd go a step further to be honest, it's not that the audience laughs because they're ignorant and think it's fine to mock the travelling community... the part that triggers the laugh is that the audience DOES know that some groups are considered "off limits" and others "not so off limits" and the immediate recognition of that incongruence is essentially the entire joke. To break the joke down and make it unfunny... it's not the community that's being mocked, nor the holocaust, it's the selectiveness and hypocrisy that we all know is very real in society. It's social commentary through satire. I haven't actually seen the show though in order to say if it's done well or not. As, to be fair, the level of skill behind a piece of satire really can be make-or-break as to whether or not it hits the mark.