I really don't understand this argument. I can only assume it's some sort of euphemism I don't have the cultural context to understand. Belgium is split right

I really don't understand this argument. I can only assume it's some sort of euphemism I don't have the cultural context to understand. Belgium is split right down the middle by language and culture, with many people supporting a split into two independent countries. Spain has Catalonia and the Basque country, two culturally and linguistically distinct regions that have long fought for independence. Ireland has spent most of the last century in a slow-burning civil war. Half of Germany was part of the Soviet Union until 1989. When people say that universal healthcare can't work in the US because of "diversity", what exactly do they mean by that word?