Obviously, I do not agree with the view that all cultures are becoming ephemeral. Drinking Coca-cola does not make you American any more than eating Chinese food makes me Chinese. I was a high school teacher for eight years. The achievement gaps between cultural groups has budged very little. That is because some cultures value education much more than others. Some value teen pregnancy. Both drink Coca cola. These are very significant examples of diversity; they have a huge impact.
You may say that all cultures will inevitably agree that education and low teen birth rates are the goal of life and what they wish. You are not the only one to posit the idea that all cultures are becoming one. But when we make that assumption we assume that they are becoming united behind Western ideals. Islam will adopt a separation of Church and State. China will become a democratic respector of human rights. Even if you believe that we are destiny, I do not think this is what they would say. As China gains in power they are increasingly unwilling quietly accept scold for not adopting Western "Universal" values. Islamic countries are not giving up. Until they give up the "illusion" of keeping their culture, it is unsafe to assume that they are just little "modern" Americans in the making.
Interestingly, people who believe that globalization is making us and our model the international default simultaneously claim that the world is diversifying. Borders are breaking down. However, that is not true. China, Japan and Korea still only give citizenship to foreigners who marry into their culture. Even then the rights are exteremly limited. Having spent time in each, I can tell you that they are not increasingly diverse. Islamic countries are not opening up to diversity. Saudi Arabia doesn't even let in non-muslim symbols, let alone people. Africa is not polyglot. Only the West is diversifying. We are globalizing by breaking down our borders. It is dangerous that we are the only ones experimenting with dismantling our culture and sovereignty. At very least we should check this trend with more rigor than asserting slogans about "celebrating diversity."
Those who think all are the same, culture has no import and diversity doesn't really exist promote open borders. They believe that all people are Americans deep down. People come here in droves; but not necessarily because they love the U.S. They want the money. They take welfare, don't pay taxes, and send their profits back home. This does not show overriding concern for America. It is not certain that we can maintain a first world economy on such a basis. Worse, many people who come here settle in enclaves and are actually hostile to the West. We do not see that so much in America yet. But Europe has no-go zones and Muslim enclaves where hostility to women's rights, freedom of speech, and the separation of church and state are not believed in.
Racism is stupid and dangerous. Because of this we have become afraid to speak of cultural differences. This is behind much of the reason that we have gone for multiculturalism. We have decided not to judge anything; to just, as the slogan goes, "celebrate diversity." It is not healthy to be blind to basic truths. Cultural diversity exists and it is important. Racism is totally irrational and dangerous. Culturism is necessary. Multiculturalism has robbed us of our ability to make value judgements. Culturism can restore our ability to make value judgements. We will have more realistic and productive debates if we identify ourselves as "culturists."
PS Culturism is defined as saying that cultures have a right to define, protect, and promote themselves. It respects the sovereignty of Saudi Arabia, China and Iraq. By definition it is not globalist, pro-sovereignty, and against attacking other nations in the name of Western - what non-culturists mistakingly call "universal" - values.