I hate "fence sitting" but I understand both sides of this debate.
The Irish have endured ridcule and discrimination for a centuries. While it is less common now, I clearly remember being infuriated by constant "put downs". There is a grey border where fun and jest become insulting and demeaning.
The thread, "Why are Americns so fat?" was such a silly statement that I naturally assumed that it was "a bit of fun". Particularly as the USA is such a powerful and successful nation, I did not stop to think that many may be offended by such.
So, I think there is no real answer. Much humour is based on exposing the weaknesses in people eg., slapstick, satire, etc. Charlie Chaplin portrayed a pathetic but loveable character. The Irish were portrayed as pathetic but loveable (sometime not so loveable) characters. One instance funny, one instance racist.
If we TRY to treat one another with respect - that is the best we can hope for. The "Fat Americans" thread started an important debate but certainly the title was insulting to some. But even if the debate had a different title such as, "Does the USA consume too many resources?", many people wold be offended by the inplications in the question as well as many of the resulting comments.
My opinion therefore is that debate on all and any subjects is important but we should always respect the views and sensivities of others. Is there a thread prefix "Fun:"? so we can distinguish humour from "Breeze Shooting" or is this going too far? Can we as adults be trusted to contribute to an open forum without degenerating it into an "open slagingmatch"? Certainly, the folk tradition has explored and influenced every subject known to man and it is only natural that contributors to the forum will whish to discuss them again online.
The kind people who provide this venue have acted as generous, even handed and openminded hosts. If we respect the guidelines which they have set out and the example they have given over the years then we will have an excellent base to work from.