Most of those jobs can be performed as well, if not better, by people with an undergrad degree, possibly with a master's tacked on + equiv number of years on the job for experience as opposed to the Ph.D.

If I were the federal budget czar, I would literally pump tens to hundreds of billions of dollars into opening national labs and hiring these STEM postgrads to do basic research. Figuring out how to efficiently produce something like high-temperature superconductors, carbon nanotubes, fusion power, carbon sequestration, gene therapy, etc. would solve some very fundamental problems, likely produce a huge return on investment, and gainfully employ thousands of highly educated people who are woefully underutilized. Even less outwardly ambitious research can produce value: look at what happened when the federal government wanted to build a more resilient computer network for DARPA.

But I’m not that czar, and I think subsidizing people into career dead ends is something we could stand to do less of.