True, and in the past it's always worked, in general, that the jobs lost were replaced by on average better jobs.
Unfortunately, past performance is no guarantee of future performance.
Most of the new jobs created by automation are quite literally beyond the capabilities of those laid off from the old jobs. As an example, it is likely most jobs based on driving vehicles will disappear relatively soon as vehicles drive themselves.
How many truck drivers can be effectively retrained to write apps for the iPad? Not many.
I cannot prove it, but I suspect our economy will become more and more productive at producing "stuff," but each year fewer people will be required or capable of doing the work that is still in demand.
People generally forget that 50% of the population is of below-average intelligence, and each year I believe there will be reduced demand in the market for workers of below-average intelligence.
But I hope I'm wrong.
Maybe, maybe not. But as jobs become more intelligence-based, persons who cannot adapt disappear. At any rate, that is what happened in the past. Many people today who lack the mental or physical resources are kept alive by the state. Is that what we're headed towards? A society that relies on 50% to produce because the other 50% can't? Time will tell.