I don't think America (the U.S.) can be said to be truly multi-cultural in as much as the emphasis is on assimilation rather preservation of cultural heritage (the melting pot).

In a multi-cultural society, each culture is encouraged to preserve their own language, traditions and beliefs while respecting others. The common society is governed by laws which apply equally to all cultures within the nation.

Yes, there is an American (U.S.) culture and many sub-cultures within American culture but they are not equal to the dominant American culture. When a person from another culture adopts the customs of the dominant culture and rejects their own, they become assimilated. It was once thought that assimilation was the answer to harmony but studies have shown that it is far better for individuals to retain their own cultural identity while living in a multi-cultural society. This promotes strong family ties, language skills and security for the individual.

Cultural genocide occurs when the dominant culture forces a distinct culture to assimilate.