But what gets built, and who benefits? And what happens to the people who were digging ditches? Does anyone care? Is it enough to wave our hands and say that statistically people like them will be better off in the future?
Well, what responsibility does an employer have to an employee? Is it a paternalistic relationship? Once you employ someone, are you thereafter responsible for their well being for the rest of their life? Or is it an economic transaction between relative equals, where either may end the relationship and go on their way? Or something in between?
In my mind, it's more the latter. The ditch diggers are grown adults and should be capable of taking care of themselves.
The paternalistic approach has been tried, but it has some unpleasant side-effects e.g. Ford spying on his factory workers to monitor their behavior in their off hours. Personally, I'd find it infantilizing.
From the employer's perspective, it's not much of a choice. If a steam shovel exists, you can buy one and lay off your workers, or you can wait for your competitor to buy one and put you out of business, then you lay off your workers anyway.
I think this is a good question. It really made me think. Why did we invent a steam shovel when it put so many ditch diggers out of work?
I think the answer is because you can build things with a steam shovel that you could never, ever build digging ditches by hand.
It may not be immediately apparent with some forms of automation, but I think that's the driving force behind all technological progress.
What if we want to deliver nutritious, affordable food to every person on the planet? Is that economically feasible with having a part of the supply chain rate-limited to a human capacity? I don't know, but I think probably not.
In the short term, some people might be out of work. In the long term, even poor people today have a higher standard of living than the richest people of a couple hundred years ago could dream of.