The overwhelming majority of us would be pleased if smart people did their work anywhere they find accommodating. Why should it have to be in the USA? Science and tech innovations are quickly shared around the world in the present day.

And the present system means that Americans are almost entirely blocked from pursuing careers in science by the awful economic prospects. Foreigners that come here can always get good appointments back home that will support a family if they can't get tenured in the USA. Americans would be out of work with zero savings and mediocre prospects at 40.

If you think Americans have something valuable to contribute to the world of science beyond than our cash support, then you can't support the level of mass foreign migration into science schools and professions.