I think part of the problem in this thread is that we're not all talking about the same definition of multi-culturalism. We seem to have two seperate schools here:

1) Multiculturalism is the addition of cultural traits from outside peoples into the existing national culture. Essentially adding new aspects to the existing ones.

2) Multiculturalism is the independant existence of multiple cultures in the same nation.

Most people seem to be saying that #1 is good and #2 is bad, but we're using the terms differently and getting confused.