Unity in diversity, is it practical ?

One of the founding principles of Union of India is the notion of Unity in Diversity. This is one of those utopian principles of Jawaharlal Nehru. It's a different story that Morarji and Shastri debunked this principle and tried to impose Hindi in the southern states which then fueled the rise of the kazhagams in TN. But my question is this Unity in Diversity concept really workable ?

When Mayflower docked in the Eastern Board, the first thing that the immigrants to the new land did was to ditch their previous identity. Many of the last names like Johnson, Richardson etc were created on the fly because the new land required them to do so. These immigrants did not try to keep their Italian roots or German roots but rather exerted extra efforts to blend in the society. Many of the biographies of famous first generation Americans would have stories about how their parents forebade them from speaking the language of the land they came from but rather encouraged learning of English. Clearly here we have a group of people who thought the best way to build a country is to leave their roots, forget their ancestry and join the melting pot. These immigrants were mainly responsible for the development of United States and its subsequent ascendence as a super power.

This same country is now in the throes of new immigrants hopelessly clinging on to their old culture. Not only does the Govt. encourage the preservation of "culture" it also encourages a multi-linguistic scenario by making spanish and other such languages as medium of instruction in schools as well as the language of choice in governance. Will this departure from insisiting on shedding ones identity and joining the mainstream to encouraging one to keep their distinctiveness cause the slow decline of this country ? Is this another experiment in Unity in Diversity ?

My personal point of view is that it is a mistake on the part of US govt. to encourage such multiculturism. History has proven that the survival of any nation state depends on its citizens feeling culturally bound to the land as well as to its other inhabitants. Multiculturism certainly is desirable by all and that's why it is gaining popularity but it will be a drag on this country a generation or two down the road.