That is an excellent point; sadly, it is one which the federal government fails to grasp. A united nation speaks a single language, and thinks in a single language. This extends to the various dialects of English, as well; for example, someone insisting upon speaking in Ebonics is not going to share the same values as someone who at least tries to speak and write in proper English. Multiculturalism always has and always will fail, no matter where its implementation is.
Multiculturalism is a dilution all the respective cultures. Even if you could assure the best of each was only brought to contribute, there are just some very fundamental conflicts between them that will only bring internal conflict.
The same thing goes for “Diversity”.