Actually, the historical Millet system under the Ottoman empire went quite a bit further towards 'multiculturalism' under some dimensions, with different commun

Actually, the historical Millet system under the Ottoman empire went quite a bit further towards 'multiculturalism' under some dimensions, with different communities literally getting their own systems of laws. But this strongly conflicted with the nascent notion of the unitary nation-state, much to the Ottoman (and Austrian) Empires' later detriment. To be clear, I'm not claiming that there aren't multiple cultures in the West - just look at Amish or Hasidic communities as examples - just that they are still forced to abide by majority rules, which necessarily means that their cultures are somewhat abridged and shorn of their full representation. And note how small these communities are compared to the majority. It's a rather different story in countries with multiple cultural groups with comparable demographic power, such as the former Yugoslavia, which was torn apart by these divisions. Put under a different perspective, you can make a rather strong case that cities and rural areas are now different cultural zones in the US, and the intractable political conflicts over abortion, marriage, and even tax policy are byproducts.