To your point about demand: there already exists (in some fields at least) certs you need to legally do certain types of work. To the best of my knowledge, only a certified PE can sign off on a bridge design, structural analysis, etc.
To your point about unemployment and the glut of STEM grads:
There's two things going on here: whether or not we want STEM grads, and whether or not we want to employ them.
I posit that yes, we want STEM grads. Unless you want to go into academia and focus on the humanities (and in turn deal with the circlejerking that goes on there, or at least appears to go on there; there is a credible case to be made that this is true) STEM is a baseline training you must have to not end up in the service industry. You learn to create things--real, tangible things that progress the race--or you're ultimately fucked.
We can't with a straight face recommend that our kids become English majors or medieval studies majors in this economy--I'd encourage my kid to take those courses on the side (you always need breadth!) but not to forsake an employable skill set. There will always be time for reading, for books, for learning and arguing and doing all those things that make the humanities wonderful and rewarding; picking up an education in hard sciences or engineering is hard, and should be attempted because it doesn't lend itself to being a hobby.
So, no, I think the push for "we need a larger pool of nominally-capable STEM grads" is totally reasonable.
The other question, though, is do we employ them?
The difference between a competent engineer and an awesome one (substitute coder, developer, or whatever) is huge. It makes sense that an innovating company is going to want the best of the best, and that thus we expect the employment percentages to reflect that. As for the blub programmers, there are many companies that are past innovation and thus can use ass-in-chair devs to maintain their COBOLS and SQL queries. The existence of the large STEM pool helps the long-tail of companies that need those okay devs.
I think it's a really complicated subject, and there is a lot to explore.
I'm more concerned, honestly, with the seeming derpiness of our brethren in regards to politicizing their self-interest: shit like the DMCA, state taxes on net commerce, etc. all seem to fly because the tech industry (rivaling if not exceeding energy, healthcare, and finance in importance to the US economy) doesn't protect its interests. For fuck's sake, it's like we're still the stereotypical 20th century nerd picked on in school and letting ourselves get bullied by the status quo. I'm more worried about us growing a collective spine than getting screwed by a .biz/.gov/.edu conspiracy.