Culture isn't "real". (part 4)

In rereading Muller's Us and Them article in March's Foreign Affairs, and the article in response, Is Ethnic Conflict Inevitable?,  in the July edition, I was struck by this passage by Muller-

There are categories of self-definition that are unfamiliar or uncomfortable to some people's sensibilities - including ethnonational identity, caste (common in India), or tribe (common in much of Africa and the Muslim world). But the fact that some people may find these categories unreal (since they know that beneath the skin humans are ultimately the same: put them in a room together with a game to play, and see how little they differ) does not make them any less real to those who believe in them.

For a fuller context, you'll have to read the articles. Muller points out that Americans (like me) have a harder time understanding ethnic division as a problem because of our relative success with accommodating and assimilating ethnic groups in our society. Granted, we've fought a civil war, had a long period apartheid following a longer period of sanctioned slavery, and bouts of anti-immigrant sentiment, but over time there has been an arc of progress; we are the first universal nation. He further cites the current "comity of contemporary Europe", though the theme of the whole article is that this comity was only made possible after ethnic disaggregation. Friends of mine have pointed out on several occasions the pitfalls of thinking certain cultural differences aren't real. Point taken, however...

Doesn't Muller acknowledge that these differences aren't real, but they are only perceived as such? I know, I know, perception is reality and all that. People act on these beliefs in a real way. I'm not an idiot, I know, in fact, that millions have died due to these perceptions. I know. However, that only prods me further into thinking that something fundamental must change about this. Shouldn't we take seriously what is real and what is not? Don't we continue to make huge mistakes over and over again by not recognizing what is real and what is not? The fact that we are all human seems paramount to me. There needs to be an effort, (a school of thought, a think tank, an international organization), that works to shift world understanding of this concept.

Instead of dismissing the American experience as an oddity, and stipulating all the greatly terrible contrary examples in its history, isn't there something in that experience that can be of value in making progress toward a peaceful One World?