Another great result is that U.S. businesses now have enormous markets in China and India in which to sell, vendors from which to buy, and more talented employees which to hire. China and India are the top two markets in the world for many products, including cell phones IIRC. Imagine the impact on the bottom line of SV companies if they went away. A smart businessperson wants other businesses to do well; they want rich, successful neighbors; otherwise, who do they sell to? Who do they hire? Who provides goods and services to them?
Yet another result is that those people are familiar with the United States and its values, and can bring them home. Wars start because political leaders can propagandize about how evil the <other people> are, which is hard to do with populations that have direct experience with each other. And the values of democracy and universal human rights (i.e., regardless of political borders) have revolutionized humanity.
And finally, due to immigrants the U.S. has become the academic center of the world. You may notice that much of the great scientific work before WWII was done in Europe, but then nationalism and ideology in Europe chased out their great scientists, who emigrated to the U.S. English become the language of science. The halls of U.S. academia have been filled with immigrants since then. If the center of knowledge and research moved someplace else, the U.S. will have lost what has really become an enormous, and really an unfair benefit. How much does SV benefit from all that research, talent, and knowledge at Stanford and Berkley?
So I want more immigration, more opportunity for more people. How absurd that people with the talent and drive to get PhDs would never have had the opportunity. If the U.S. has to build more universities, that's great.