If 'Death to all jews' -- let's not talk around it, that's what was written on the sign -- wasn't the crux of the joke, why didn't he go with something equally likely to be rejected by people who understand English, but less 'Death to all jews'? Frankly, I think it's because he's a moron who doesn't understand that actions and words, however digital and remote, have consequences. Now middle school kids can chortle together on the playground, "haha, 'death to all jews', that sure was funny". After all, the life or death of a Jew, that's just a punchline.