The theory only says that all the people globally will be better off. It does not say anything about citizens of a specific country that is applying protectionism. They may be better off for it, they may be worse - it depends on the particulars and, as most economic interventions, can only really be judged post-factum.
I don't think unionizing will help with off-shoring for development. I do think unionizing could bring about more equal treatment though. It seems most companies ignore their own policies when it comes to ratings, work assignment, hours, etc. Devs have very little recourse. Of course the assholes that do well and aren't afraid of c grade coders are the ones who don't want unions since they might loose their edge over others comp-wise.
Consider the common refrain: I'd rather negotiate for myself
It's like, a fundamental misunderstanding of how power dynamics work, as if you as a solo person in a 1000 person company could somehow EVER be more valuable to the company than the entire labor pool.
Newsflash: If your company doesn't throw a fit any time you try to take time off, like CEO comes and talks to you personally fit, they think they could replace you just fine. 40 years of project management has attempted to build things just for that.
The misunderstanding is yours. Workers understand what you say just fine, but don't care about out-negotiating the company. They will never meet the CEO at the bar, so it means nothing to them. They want to be able to out-negotiate their neighbour so they can peacock dominance over someone they actually interact with.
The purpose of a union is to establish a brotherhood between metaphorical neighbours so that they don't try to be assholes towards each other. While that does, indeed, improve the overall worker position against the company, it hinders the power dynamic between them. And that's where you find the pushback.
It's much like you find in 'middle-class' neighbourhoods where you see households trying to outdo each either with nicer yards, or fancier BMWs, or whatever, all while racking up crazy debt to pay for it all. If they invested the money they pour into that stuff instead they would be way better off, but being better off isn't the motivation.
Is it still forgetting if it never happened? Both the idea of the 8-hour work day and weekends predate the first recognized union. The 40-hour workweek became the norm during the Great Depression by way of government initiative in an attempt to spread the work out across more people.
Unions have long supported the 40-hour work week, but are not meaningfully responsible for it. If showing support for something is necessary for something to exist, then you could probably say that just about everything exists because of unions...
Even still, we're talking nearly 100 (when it became common) to well over 200 years ago (when it was conceived). Even if unions actually were responsible, people are going to naturally ask "What have you done for me lately?". Where is the 10-hour workweek?
Besides, let's say youre right and unions have given us all those things. Those standards are over 100 years old. If it were true, it would mean nationwide unions did some things 5 generations ago and have collected literal trillions in inflation adjusted dues* since and have provided nothing in return.
* 11% of the US is unionized, representing about 1.1 trillion in annual payroll. Average union due is 1.5%, that's $16.5B per year in union dues collected, over 100 years = $1.6 trillion. But union membership used to be much much higher than 11% so its actually a much bigger number than $1.6T. But you get the math.
The metrics do not show the American worker being better off after these policies you support were enacted and have had decades to run. Free trade is great for shareholders and some consumer cohorts who get excess utility, but terrible for workers.
https://www.epi.org/publication/briefingpapers_bp147/
https://www.epi.org/publication/botched-policy-responses-to-...
https://www.epi.org/press/globalization-lowered-wages-americ...
https://www.npr.org/sections/thetwo-way/2015/12/09/459087477...
Eh, maybe not. It depends on the demand and availability of skill/labor. If you have a high percentage of low skill labor and you can outsource low skill labor to cheaper markets, then what are the current low skill citizens going to do? Surely the rust belt is not better off now than when coal and steel (and other manufacturing) were still a domestic thing. Maybe other areas of the county faired better, but with median wages dropping over the past 50 years, it doesn't seem like a strong case.
You're almost certainly correct in the sense that the people of the entire system will be better off, but your own domestic market could suffer at the gain of the other market where the business is now being outsourced to.
A good example of this might be tech in the EU. The EU basically has no major tech companies because we "import" all our tech services the US (Facebook, Google, Amazon, etc). It's great for us in the sense that we didn't have to pay anyone to build amazing online services like Facebook, Google, etc – it's just free stuff we get here from the US. But who benefits the most from this arrangement, is the US or the EU? I'd argue that the EU allowing the US to provide all of our major tech services has been great for US growth, but it's stagnated the EU economy in recent years as we've had no real reason to build 21st century companies here. The free stuff we get from the US actually comes at a cost for us even if overall the economy as a whole (EU + US) is better off for it.
Similarly, imagine an extreme scenario where US companies outsource all work to low-cost labour countries (I know this is impossible, but assume the US is 100% service sector jobs which could be outsourced). Would this hypothetical scenario be good for the US economy? It might be good for companies registered in the US because now they can provide their services to markets they serve for a fraction of the cost, and it would be great for those low-cost labour countries getting all this foreign work, but it would be awful for the actual US economy that's allowing this to happen in the pursuit of efficient markets.
So yeah, you might be growing the whole pie at a faster rate, but it's possible mass outsourcing doesn't help grow your share of the pie. And like with manufacturing, you also need to consider how you'll lose technical competency within your domestic market over time if you outsource too much, and this will likely lead to the country you out sourced to eventually out competing you in your own industries. We see this today in China.
If you want to cripple tech innovation in the US, outsource all your software engineers so there's no one in the US with the skills or resources to start the next Google or Facebook.