Lexicus
Deity
stuff
So, I found this to be an interesting an largely accurate post (I edited it to "stuff" here to save space), but I think it misses a few things. One, when most people think about "multiculturalism" they aren't thinking of it in terms of 20th century liberal sociology etc. In my experience most people who are for "multiculturalism" (at least in the US, I suppose your experience in Europe may be very different) simply mean that they want a multiracial society in which "whiteness" is not automatically seen as hegemonic. I agree that discussions of culture are very frequently tied up in race, to the extent that much discourse about culture is actually just discourse about race with a few words changed around.
The "salad bowl" vs "melting pot" idea, in the US context anyway, I think generally also refers to this idea of hegemony of certain cultures. People who argue that immigrants should "assimilate" are arguing for their own culture (or rather, their own idea of what the culture of their country should be) to remain hegemonic. The fact that immigrants inevitably assimilate to a certain degree is beside the point.
In the US this is all so tied with race that "multiculturalism" is a good proxy for anti-racism, or at least for some sort of multiracial democracy, while those opposed to multiculturalism are (in my view anyway) generally just racists of some kind who are either for the outright exclusion of non-whites (the more anti-immigration segments of the Republican Party typify this tendency), or at least for the maintenance of whiteness' hegemonic position in a cultural hierarchy where cultures defined as "other" are marginalized (this is still arguably the "mainstream liberal" position, and was certainly the "mainstream liberal" position for much of the 20th century).
Religion doesn't fit your model very well.
Uh, yes it does? Sharply defined religious boundaries are the historical exception. The rule is syncretism and coexistence.