The USA is a nation founded on an idea, that all men are created equal, and despite peiods of xenophobia and know-nothingism, has pretty much maintained a policy of openness to newcomers from just about anywhere. When Americans talk about their "nationaliities," they are usually referring to their ethnic background, the nation(s) from which their forebearers emigrated to America.

The upshot is that the US has to face up to arguments about "multiculturalism" to an extent that no other nation on earth should have to. There is no conceivable reason for, say, France to give up French customs and holidays, Germany to "downgade" all things German, etc. Modern industrial nations, of course, customarily maintain an open door to immigrants, if only because there are some low-level jobs that natives won't fill, and therefore have an obligation to provide a somewhat welcoming atmosphere.

So should it be for Great Britain, but apparently these days, to some folks, it's not like that at all, and Bristish society is supposed to be equally open to all comers.

One mitigating factor, I would guess, is that more than one "nation" (in the ethnic rather than the political sense) in included in the United Kingdom. Despite centuries of interbreeding, there remain differences among the English, Welsh, Scottish, Irish, and Irish/Ulsterite. Or, at the very least, differences beteen the Anglo-Saxon and the Celtic. Of course, all these groups are nominally "Christian" (or ex-Christian), and accustomed to Christmas in both its spritual and secular incarnations; there are no Mohammudans or Shintos, etc., among the competing tribes and clans native to those islands...