North African Muslims can move to Holland en masse, remain Muslims and North African, and be "Dutch".
Caribbean Blacks and African Blacks and Asian Muslims can move to England en masse, remain so, and be "British."But consider:
Han Chinese move to Nigeria en masse, maintain their race and language and culture and be "Nigerian."
Germans, Norwegians, Russians, Brits, and Belgians move to Italy en masse, and be "Italians."
Is the whole idea not nuts? You'd have to be entranced by a cult to believe it.