The survival of any race or ethnicity depends on a couple of factors; one of which is to be attracted to your own. This means that they must consider their own features better or superior to other races. The simple fact is that an individual can never like different sets of racial characteristics or features equally. For example, I am primarily attracted to women of my own ethnicity or Caucasian women in general. This does not imply racism in anyway whatsoever since all races & ethnicities are naturally or by default attracted to their own. That is one reason that the world can never have a single standard of beauty. Most ancient cultures had their own standards of beauty, & for the most part, many of our countries do celebrate the beauty of our own women. Apart from that, the vast majority of people prefer to have children or descendants that resemble them.
I am not saying that people should never marry those from other races. Indeed, some men & women may prefer spouses from other ethnicities, & if they are able to find a good spouse from another race, then good luck to them. However, such marriages or relationships should never be promoted & nor should they ever be the norm. That will lead to nothing but the destruction of that race & culture. Usually, only those suffering from self-hatred & low self-esteem marry outside their ethnicity. Another interesting point to note is that having a strong national or ethnic identity aids in preserving racial & ethnic identity. This is the reason you won't find many Middle Easterners or South Asians marrying outside their ethnicity. They are proud of themselves & their heritage, thus they seek to preserve it. In any case, good luck to the newlywed couple.