FWIW, I went to parochial schools, 1-12, in the fifties and sixties, and I was taught that "melting pot" was a pejorative or sarcastic expression. The ideal metaphor was "mosaic," where elements of the native culture are retained during assimilation, thus creating a colorful fabric of society. Pittsburgh, my home town, has (had) a score of different ethnic neighborhoods, all with their own churches, social clubs, and businesses. We still have churches that were overtly and proudly built by German immigrants, Poles, Ukrainians, Slovenians, Chinese, and so on.
But they all knew what team they were playing for. When it came to war, they volunteered in massive numbers - even Germans - to serve their adopted country.
Would the same thing happen now with the Iranians, Syrians, Serbians, and so on?