If the races of the world cannot get along on one planet how are they to get along in one country?
The great American melting pot is having a melt down due to two things.
The huge change in our immigration policy that reduces the number of people from Europe while opening up the floodgates from third world countries that do not share our culture, values and heritage.
Everywhere we have influxes of immigrants from different cultures, there is always conflict. My example is Oslo Norway. I was there in 2004, it was a fine city, clean, little crime, quiet. But in 2011, I saw how the migrants from the middle east and Africa had destroyed parts of it. Litter everywhere, and crime had gone up quite a lot. Is it because of skin color? Of course not. It is because of culture, religion, language, that sort of thing.
We are told that diversity brings peace and tolerance. We are told that places with many ethnicities and religions will be culturally enriched. This is a lie. Let's take a look at some diverse areas. First off, the Balkans have lots of different ethnic groups cramed together in a small space. That lead to multiple wars throughout the 19th and 20th centuries until the region was divided into 11 seperate nations. I guess diversity didn't unite them. How about some more diverse places, Lebanon, Syria, and Iraq. Lebanon is about 1/3 christian, 1/3 shia, 1/4 sunni and the rest druze. Syria is mostly suuni, but it also has many shias, christians, druze, and ethnic Kurds (who are sunni but identify with their ethnicity). Iraq has a shia arab region, a sunni arab region, and a kurdish region. It also has a christian minority. As you can see, these nations haven't yet realized that diversity is meant to bring peace. Another example of diversity is the "rainbow nation" of South Africa. There is an ongoing genocide against whites there, as well as attacks on other africans who immigrate there.
Are you really going to tell me that these diverse areas are more stable than places like Iceland, Japan, or Denmark? I can't imagine any sane person would make that claim.
It is in our nature to judge and act accordingly. Although it is not best to judge just by mere appearance, most if not all of humans even animals judge upon appearance. When we see someone different (skin, hair, physical/genetic) differences, we judge to see if they are like us, and it arises feeling of discomfort and for some curiosity. Initially these feelings subsides depending on the experiences on each person.
Having a society where general appearances are similar, gives us less reason to judge someone and they look like us, thus most likely act, think, or live like us, which is relatable.
However, I am optimistic of the far end result of multiculturalism. Perhaps in the far end when "races" continue mating and cultures merge, such as people as half black/white/asian/mexican/others. The "racial" differences began to collapses, as it goes back to human nature to judge upon appearance, and as we look alike "through inter-racial mating" , it should ease our instinct to judge upon difference. Although the term "race" is not a legitimate word recently, we are all human.
Nations with a singular culture/race are often the result of long term discrimination and shunning of surrounding groups of people. This negates harmony, and is instead a constant battle.
Different people are unavoidable. Strong nations need to form alliances. They need to trade goods, services, and technology to compete with the rest of the world. They're not doing themselves a favor by denying the contributions of different people, rather than putting away their pride to work for a common goal. A racist who avoids other races and calls that harmony is avoiding the more effective solution.