It's pretty simple, really...if there are a few people about, speaking a different language, or yours with an accent, cooking different foods, worshiping different gods, wearing different clothes...etc., it's quaint, interesting and educational.
   If there are a few MORE, enough so that you find them regularly in jobs where they interface with 'the public' much, it becomes slightly awkward and 'enclaves' spring up and cultural clashes become an 'issue'.
If sizable numbers develop, entire communities and nations have major problems trying to work out how to embrace the benefits and opportunities of "multiculturalism", while juggling the conflicts, misunderstandings and 'perceived' threats of having one's own culture diluted and/or changed...etc.

   Despite slogans and 'political correctness', mixing cultures too quickly and with little oversight is NOT automatically a healthy, simple process. The Japanese understand this, and consciously resist certain changes to their culture. They do NOT always do it genteelly or gracefully, but they do prevent some problems at the expense of being called 'isolationist' in some areas.

The USA was founded by many different groups..(and overran a couple others in the process!)...but the situation in 2008 is not the same as in 1690...or 1778...or 1875...or even 1912! We are a melting pot....but ingredients to some recipes need to be added slowly & carefully when everyone has to eat from it. (no extra charge for ambiguous metaphors)

It is time to look at the issue of what it MEANS to embrace multiculturalism....and how to have a serious discussion of any related issue without labels of 'racism' flying anytime a disagreement arises.

My favorite aphorism of all time:

"It all depends on whose ox is being gored."