With a stronger union movement there might have been controls put on how much labor could be shifted off shore. There might have been tariffs put on imports. There might have been public works projects established to employ displaced workers. I'm not saying that these are good or bad ideas, just that with organized labor having no clout they weren't even discussed.
Another point is that organized labor only has to be about 30% of the work force for it to create a positive influence for all workers. Non-unionized companies need to be roughly competitive or they won't attract workers. Notice also that in the few service areas where unions have succeeded they have improved the working conditions for the sector. Some recent examples: janitors, home health care workers, and hotel employees.
I belong to the school of though that says "might makes might". There are three factions in an economy: government, business and labor. If one is noticeably weaker than the others its interests will get short changed. That's what has happened to labor in the US in the past 30 years and appears to be happening in Europe now as well. Policies not Politics ---- Daily Landscape