I worked for 30+ years in a large manufacturing plant. (I am now retired.) The peak employment at that site was almost 24,000 people in the early to mid 1970s. The plant now employs well less than 5,000 people.
The output per employee (in terms of finished products) is much higher now than in past years, and improvements in productivity are partially responsible. A much larger reason is that almost all of the parts used in the plant are made elsewhere, many of them in Mexico, Central, or South America. When I first started working there, almost all of the parts were made in house. Essentially, the site is just an assembly plant now.
Of six main manufacturing buildings - once all full - two are now vacant, and three are only being partially used.
There are two auto assembly plants in my city. I took a tour of one of them a few years back. Engines came from Germany, transmissions from Brazil, axles from Mexico, smaller parts from all over the place. Yet this is supposed to be an "American" auto company.
So, who you gonna believe, your lying eyes or this shill? We are still a great manufacturing nation. Yeah, right.
So now you have the dirty repetitive labor done for a lower cost in Mexico, leaving the relatively better assembly work for a smaller number of American workers. But the question is, what happened to the American workers who were laid off as a result? Were they hired to do assembly work at other companies that were started because inexpensive Mexican labor made such companies possible? Or did they become burger flippers?
That’s the crux of it IMO. I don’t see a problem with sending dirty/boring/repetitive/polluting/dangerous manufacturing jobs overseas as long as there are better jobs being created over here. And I don’t see a reason why that can’t be the case. Sending a manufacturing job overseas creates an opportunity for a foreign worker and frees up an American to do something better. But we gotta make sure the better exists.