Every once in a while, I read some article about the ratio of international students: domestic students in STEM schools. If the general public can comment on the article, you usually get a lot of rants about how international students are stealing opportunities from domestic students.
Here's the thing: in a lot of these departments they can't find enough American students to fill the openings. I'm familiar with one engineering department that didn't have a single non-international grad student in the entering class for the next year. They're desperate for Americans because, frankly, those statistics look really bad. And they want to educate Americans. But trying to get an engineer in this discipline in for a masters or PhD is nigh impossible because they can earn tons of money right off the bat, without going to grad school. Same thing for a lot of math and computer science departments.
We don't live in a vacuum. Everybody wants the US to keep its technological superiority. And to do that, you have to compete with a lot of upstart well funded universities. If we aren't raising the numbers of scientists and engineers we need ourselves, we're going to have to take the best and the brightest from the rest of the world.
I do think we have a culture against STEM education - the popular conception is that all STEM folks are hopelessly nerdy white males, and smart, ambitious people people here tend to gravitate toward better paying and more culturally accepted work. We do need to improve the STEM pipeline, but in the meantime we're going to have to supplement with non-Americans to keep our competitive edge.
I think international students are a net positive for grad schools in other ways, but that's another post.