Let's match your anecdotal evidence with mine. I am an H1-B visa holder; furthermore, I am also an electrical engineer that works as Digital Lead for my company. Why? Because they couldn't find an American with my qualifications or education background necesary to fill in the post. Let me rewind back a bit to my commencement ceremony. Out of 1034 students at my university, only 34 were engineer graduates. 6 were electrical and not one was American, we were all foreign born from Latin America (me), India, and China. The other engineers for other majors? Only 2 were American, and they obtained Civil. The rest in the ceremony? Well, they were all Business, English, Geography, Fine Art, Photography, Education majors and yes those were filled with Americans. Funny story.
Oh oh! Forgot to mention, I graduated in 2011, but trust me, things haven't changed much.
See above. Or rather, just go to a campus, you won't see Americans doing STEM. Or if you do, they are all freshmen/early sophmores who eventually drop out into business or some other Liberal Arts degree. See above.
You apparently have no idea how bad this move would be or how dire the consequences can be.