I have a piece on this in National Review Online today (based on a 2008 post). Here are the opening paragraphs:
People talk a lot about “multiculturalism,” whether to praise it or condemn it. But standing alone, the concept is too vague to be supported or opposed. In this respect, it’s much like certain other concepts, such as “equality.” Do you support equality or oppose it? Well, it depends on what exactly is meant by “equality,” doesn’t it?
“Multiculturalism” is similar. Some things that are reasonably labeled “multiculturalism” are mostly bad, and others are mostly good. We can all imagine bad versions of multiculturalism — ones that dramatically undermine the social cohesion necessary to maintain order or defend the nation in war; ones in which many people in a modern economy speak mutually unintelligible languages; ones in which members of some subcultures feel comfortable violently attacking people, whether of their own culture or of others; and so on. But America is also founded on its own sort of multiculturalism, which has usually (though not always) stood us in good stead. Here are four constitutional manifestations of this multiculturalism.
For more, see here.