As if that ever stopped anyone... Just because it's not allowed doesn't mean it won't happen. Especially in a heated discussion where one or more people end up pissed off. (which happens practically every time you discuss politics with people in a global chat) It just gives staff more to watch out for. It's stupid.
It WILL get out of hand though - That happens with all political conversations on a large scale in an MC server. Why do you need to talk about it in global when you can just do it in party chat or PM?