The U.S. should be doing their very best to have the strongest possible education system for all its citizens (and non-citizens living in the country long term). As should any reasonable country. But the fact remains that, unless you are counting with excellent execution in that regard from the U.S. and abysmal negligence from the rest of the world, you simply can't extract the same talent from a population of 400 million than from one of 7 billion. The U.S. benefits enormously from immigration, in ways many don't even perceive. If the flow of minds into the country is ever truly stopped, no amount of improvement in the internal education pipeline will be enough to maintain the U.S. dominant position in science and technology.
Now, you might be ok with a broader geographical distribution of this type of talent, or argue that it will happen eventually no matter what. I hear you, on both counts. But, as a non-U.S. citizen, I am actually pretty surprised that the country would chose to forgo the advantage it enjoys by being a preferred immigration destination for so many skilled people...
It also seems to be done due to nothing but rank xenophobia. I mean, what is the excuse here? "They are stealing our jobs!"? This is literally a visa where the requirement is to create jobs for American citizens, and most of these tech firms will do so by exporting goods mostly to foreign markets (the market for most tech startups is not over 50% local to the U.S.) and/or creating local technology and expertise. Hell, once profitable, you can and should tax these companies to help provide for that very same education you want for American citizens! As well as UBI for those whose jobs are being displaced by automation. Startup visas are as win-win as it possibly gets.
Final point: The party and particular administration that seems to be most against immigration also seems to be the one most against science or robust public education. The foreseeable end result is grim, even if these policies last only 4 years: a "lost half-decade" in which the best domestic talent is under-nourished and the best foreign talent goes elsewhere.