It does allow the management class to enrich themselves, but I've observed it enriching the foreign working classes tremendously. The reason 'slavery' level wages are able to compel foreign labor to come to cities and work in abhorrent working conditions is because it's better than what they had before. And as they gain experience and education, it's always cheaper to train the locals than it is to fly in the Western experts.

I'm a controls engineer who installs industrial automation for manufacturing and testing. Most of my customers have headquarters, R&D, and some manufacturing in the Midwestern US (especially Detroit automotive companies) but many have expanded to add Mexican or Chinese factories. I've worked with, trained, and socialized with a ton of operators, technicians, engineers, and translators (my Spanish is passable, my Mandarin is abysmal) in those countries just as I've worked with their equivalents in the US. My observations have been that when American companies add overseas manufacturing, sure, the American management siphons off what they can, and I'm extremely dubious that this money is legitimately proportional to the value that they add to the stream instead of the wealth that they have power to extract, also, there are some growing pains of exploitation and pollution - but the overwhelmingly more powerful effect is the growth in the foreign town where the new factory is installed.

Time and time again, I've talked to people whose parents or grandparents were practically subsistence farmers, but now they're happy to be English-speaking engineers, members of the global economy, possessing more wealth than many generations of their ancestors could have dreamed of. You're familiar with the American phenomenon of disenfranchised Millenials still living with their parents with (or without) a minimum-wage job and college debt who are unable to afford to live on their own... In Mexico and China, the opposite is true - the parents have no money, and have never had money, instead, whole extended families are living with their children who have foreign money and modern luxuries like medicine, air conditioning, and automobiles. It is true that this unimaginable wealth is initially earned by the children at something on the order of laborers at $5/hr and engineers at $20/hr, which would be criminal in the US, but (1) those salaries grow far more rapidly than American minimum wages as the workforce gains education and experience, and (2) the purchasing power of that amount of money is far higher in those countries.

Their living conditions have gone from that of villages that wouldn't be unfamiliar to someone on the 17th century American frontier, to something more like the 'bad part of town' in a 21st century American city. I agree that it would be better if they were in conditions like the good part of town. I agree it's inhumane to take more than your fair share of the revenue out of the hands of people making $10k/year. I agree that we could do better to ensure this doesn't happen with slavery and pollution taxes. But I also have first-hand communication, albeit in my second language, that the resulting situation is better than erecting barriers to trade and leaving them alone.