In America there's a very sharp geographical distinction between which people oppose the melting pot and which see it as a core part of the American experience.

People from the big immigrant cities like NYC, SF, LA are more likely to hold the latter position.

People can feel how they want to feel, campaigns are run on feelings and not facts. Just because Trump says Haitians are eating cats and dogs doesn't make it true.

The Mormons of Utah, the Cajun/French of Louisiana, the Norwegians in the Dakotas, the Scotch Irish of everywhere, and the Amish are all (non-brown) examples of enclaves existing in the US. Nobody says that they are not assimilating well. We let them live their lives because personal liberty used to be a thing here.

A large number of those people are only a few generations removed from immigrant ancestors.