And that such a choice can be made means what with regard to racial characteristics?
That the differences are somehow arbitrary because you simply regard them as different branches?
I am not married and I am not really mindful of the social effects. To me, marriage is only a sacrament and a sacrament I will never receive.
But I imagine there are issues in particular societies which take great prudence to address. But, if prudence as a virtue is to be lauded in this case, it must also be lauded in all other acts, and you are not prudent at all, so you cannot appeal to prudence for other people getting married.
The differences are arbitrary in a moral sense, but in particular times, places, and circuмstances, they may be more significant. The "one drop rule" in the USA for instance has a great impact on our thinking here, as if darker skin was somehow pollution.
For other places and people, there are other factors. Look up Korean issues in Japan, and you'll see an entirely different set of race issues. To you, I imagine you do not make the distinction finely between Koreans and Japanese, but it is a major issue in Japan.
Likewise, the different ethnic groups in China are major, as some laws do not apply to people who are not Han (the one child policy for one), yet, I highly doubt you would make the distinction, and prefer to see "Chinese" as one thing.
Different races in India may also be a good study, as there are variations in skin tone, but in general, they are all very similar and we would consider them one race, yet, they may make distinctions we wouldn't think to make based on social status, rather than genetics.
The world is bigger than what is in your eyes.