People who don't share the same (or at least similar) values, customs, mores, and so forth tend to separate themselves into groups of people who share their same values. We've worked too hard for too long to combat separation. Separation was once coded into law and was called apartheid. Separation was once used as the reasoning for "no coloreds allowed." There are still groups practicing separation, e.g. that LDS split-off in Texas recently in the news.
I think the "Great Melting Pot" is one of the key factors behind American's strength and success. The other, of course, being the Constitution. When we feel like we're one, then we pull together when we really need to pull together. When we're split apart, then the separate parts do their own things, go their own ways, and the strength of the country is diminished.
In America we can each be different from each other, we just don't want to be TOO different. Differences just make people uncomfortable. It's human nature, you're not going to change that. Even if you respect the differences of someone else, and they respect yours, the natural inclination is to just stick with your own group. Remember high school? Human nature at work.
You can see this in each wave of immigrants: they clustered together into their own communities. It wasn't until the second or even third generation that they got out of their protective and comfortable zones and integrated into the general social fabric. And it happened because they learned English, and picked up the customs, ideas, thoughts, values of those around them; principally in school, and later through work. In other words, they because less and less Chinese, Italians, Irish, or whatever, and more and more just plain Americans.
That process is in danger of being lost in this country.
My thoughts on the matter, anyway, since you asked.