" Somehow the "mother" of multiculturalism and the outcome is not that bad."
America was a "melting pot" NOT multicultural. America has ALWAYS had a unique culture-until recently.
"Multiculturalism," as it seems to be most accurately defined, is the parallel existence of multiple cultures within a single society.
As far as I know, no multicultural society has ever lasted very long.
The U.S. has never until very recently really been a truly multicultural society, because while there have been regional subcultures (e.g., Cajun, New Mexico, Midwest Germanic), there has always been a clear understanding of and participation in the overall American culture, and the subcultures have tended to become part of the greater culture, rather than remain truly separate.
Part of this is probably because the degree of difference was sufficiently small to allow this to occur.
The problem with today's immigration pattern is that now we have groups that have very, very great differences from the cultures/societies to which they are migrating. Multiculturalism, even if not desired, tends to be the result. It remains to be seen if such differences can be blended into the host cultures.