As far as I can see, "multiculturalism" is the belief that we should celebrate and encourage diversity because we are all really the same.

If one looks at the competing Christological doctrines of early Christianity -- Arianism, monophysitism, monothelitism, Marcionism, Patripassianism, Nestorianism, Chalcedonianism, and so on, from a modern atheistic perspective it all looks insane. Even leaving aside one's presumption of the non-existence of the relevant supernatural entities, it still looks like a mass of confabulation accreted like a pearl in an oyster, around a seed of irritation resulting from thinking about how Jesus could have been both a man and God.

So, after perusing that section of the Wikipedia page I just linked, look at the first paragraph of Wikipedia on multiculturalism.

Doesn't it look just as insane? Is "a society at ease with the rich tapestry of human life and the desire amongst people to express their own identity in the manner they see fit" any more meaningful a string of words than "the human nature and pre-incarnate divine nature of Christ were united as one divine human nature from the point of the Incarnation onwards"? What would the bishops who argued about the latter at Chalcedon have made of the former? Never mind agreeing or disagreeing with it, what would it even mean?