Leaving aside the question of what one means by "multiculturalism"--because there a lot of different ways the word might be applied--it wouldn't make sense for an establishment control measure to prevent cultural unification, when one would think a culturally conglomerized population would in fact be easier to control. Which is an argument against the Melting Pot metaphor.

ETA: That's not the same thing as saying identification with a larger crosscultural national identity is a bad thing, or even an unnecessary one. But why should peace and harmony depend on people giving up their differences/Culturally Specific Important Stuff?