But worker pay won’t go up unless there’s a shortage of workers. This is orthogonal to worker pay.
Why is this undesirable? Simple. Lower and middle class workers drive the economy with their consumption. If they don't have stability, they don't spend. If they don't spend, the velocity of money through the economy decreases. You want workers to feel comfortable spending, and the only way to do that is by giving them stability along with a fair wage.
It's possible it would be if it was more tax advantageous to pay workers then to pay out profits as buybacks through the most recent tax cuts. Clearly, taxes matter in corporate decision making, as large multinationals were keeping their cash offshore as long as possible, waiting for a tax holiday.
Social security, workplace safety, overtime ... all just magically appeared, correct?
Because maybe, again, just maybe, I'm being dense, but I don't think "skillsets" were ever a limiting factor for those who spearheaded unionization. "skillsets" are a facet of the bourgeoisie labor market, which I say as a firm capitalist. It's always been those at the bottom who have fought for worker's rights.
No. It took capitalism—more precisely, the resulting accumulation of human wealth and technology—for child labor to disappear. It disappeared when it became economically unnecessary for children to work:
http://atlanticsentinel.com/2011/01/did-government-end-child...
I am continually surprised by the number of people who seem to be under the impression that the default state of nature is one of abundance rather than scarcity. Why do you think children had to work in the first place?