The argument in the St. Onge link is so bad it is barely worth discussing,

Yeah, I often find his stuff similarly discombobulating, but this one seemed worse than usual. Perhaps audience capture at work in earnest.

First, does it seem plausible that "semi-literate manual laborers" will come with such a high demand for dentistry that it would lead to an extreme shortage of dentists?

Give em a dollar, they spend it on getting braces. Typical.

I could go on and on, but there is a lot of research that has empirical evidence for this stuff.

Thanks for the link, that's what I was hoping for :)