Having a population made up of immigrants has always conferred an edge on America, because, with few exceptions, we can draw upon "in-house" expertise with any other culture we have to deal with. Now that I think about it, you could chart our relations with the rest of the world according to which group is represented within our own power structure. We've always down well with Europe, being dominated by descendants of Europeans ourselves, and relations progressively decline (or become less certain and more volatile and prone to misunderstanding) as you go down the list of other peoples represented in America in smaller and smaller numbers. It's not an absolute constant, of course, because individuals with greater empathy (stronger theory of mind) can "imagine" how to better relate to people from "alien" cultures. Oddly enough, George Bush seems to have a powerful empathy for the Arab culture...well, that comparison could ultimately lead to CurrentEvents, so I'll stop there. But yeah, the "melting pot" is more than a sentimental notion, it's demonstrably a strength.

We're both (wisely) avoiding specifics about which belief systems are more survival-positive on a cultural level. I'd just observe that the potential disagreement is made possible by the existence of cultural diversity in the first place, and that the process of arguing about it could legitimately be included as a necessary component of the evolutionary process constantly taking place in the noosphere. Cultures that don't argue don't progress.