As I said, a lot is going on in that joke.
1) The division(s) of mankind
2) The mob mentality - i.e, *we could be like you Jimmy* so we will just pretend we are not by denouncing you as a sole deviant
3) Picking on the dyslexic minority(which is just offal)
4) Jimmy Somerville is Gay(no offense), but yet another minority group.
So lots of minorities and the fact that people love to pick on them and don't generally know of any other way to treat minorities rather than with great wrath and disdain. So all in all, quite a lot going on there.