Addressing the question in the title, "What happens if an entire class of workers loses faith in their careers", look at what happened to printers. That was a good skilled trade for centuries. Then it just went away. Phototypesetting took the high volume end. Desktop publishing took the low end. Computer-controlled presses took press operators. And then the newspaper business died. I've heard homeless former printers…
I sense there is this air around of "demand our jobs keep being relevant" - I personally feel this kind of thing holds the world backwards if it works. I think if our jobs were to become obsolete, embracing it and re-orienting oneself is the one thing that is personally effective and is morally right. But what do I know, I'm just some doofus on the internet. The irony is not lost on me on all those years where people…
If a $20000/y a job is deemed unrelevant, chances is that one might easily find similar or better in a totally different area.
If a $200000/y job is deemed unrelevant and is lost, and one has mortgage payments they can't pay with a $50000 or $100000 job, they have a big problem because selling that house might become difficult when all other $200000/y workers will try to sell their house and move within the same period and the housing market crashes. So you can ruin the economy of a large area quite quickly.
So a bit of anticipation is useful.