The real problem occurs with what I think economist call...

The real problem occurs with what I think economist call "structural unemployment" - that's when a large employer in one location shuts down and suddenly thousands of people are out of a job at the same time - eg the Whyalla steelworks, the coal power plants, a large mine, etc - which causes huge problems for the town as it cannot absorb the sudden increase in unemployment. It is fair enough to consider these as real problems.

But improving efficiency, as FBR does, only does micro changes to society which will not be noticed at all (except by those who have an axe to grind).

As you correctly say people move on to different jobs - those which are better anyway- higher pay, more intellectual, less health risk.

Also there is always a need for artisanal work - people pay a premium for high quality hand-made things. Louis Vuitton makes a fortune from $5000 handbags, whereas there are many cheap bags under $50 at KMart. So I expect bricklayers in the future will concentrate on high quality walls, and in difficult locations, for which people will pay a premium.

Nobody calls a concrete pump to do a small job.