Why does the United States allow people from all over the world to immigrate to the United States, which will lead to a very mixed mixed-race era in the United States?

Genetically, no one is pure. In the course of millions of years, human beings have mixed blood many times. The United States itself is an immigrant country. Fewer people are born than die every year, and the non-immigrant population is getting smaller and smaller. Moreover, immigration to the United States requires conditions. The poor and unemployed want to go. Some people say that TOEFL is the American harvester for world talents. The harvester only harvests the ears of wheat, and the useless straw below is not needed, as long as the elites of all ethnic groups are on the line.