The 'myth' is that long term, there are fewer jobs available because the machines took them. That is, agreed, not true on a historical economic scale.
Unfortunately, vast swathes of people are however left unemployed after huge shifts because people-jobs-geography-ability and the many other factors involved are not a free flowing system. The advent of mills had a catastrophic effect on the household income of those thousands involved in home-based hand spinning for 50 years. Historically we can say that in the end, the job market just shifts, but that doesn't change the disaster which happened to those actual people.
Like it or not, regardless of opinion, when these changes happen, although new jobs are created and are available, they are not necessarily available to the same people who lost their jobs at the time they need them. So in the short term and in specific geographical areas or groups, people are absolutely left without work.
