Here's the thing. By moving production to low-wage countries with poor environmental and safety (and other) regulations that protect people, American companies can lower the cost of production. Economic theory says this "frees up resources" in our own economy to be put to "more productive uses." Economists say the workers can thereby move into higher-paying jobs, doing things that can't be done in Vietnam.
But of course this is not what has been happening since the country's elites were sold on the "free trade" agenda decades ago. We have seen the financial sector (and its associated value system) increase as the manufacturing sector (and its associated value system) declines. We have seen a dramatic increase in inequality as the "investor class" pockets the wage and other cost differential from moving production out of the country. We have seen entire regions of the country literally devastated (see Detroit and the "Rust Belt") because the resources released by outsourcing America's production have not been reinvested in the U.S. They have instead found their way to foreign tax shelters. We have seen the country lose entire industries, and the supply chains, "know-how" and other elements of a manufacturing ecosystem that might enable us to rebuild someday.
Now that we can actually read it we can see that TPP is just one more "NAFTA-style" power-grab elevating the "investor class" above the rest of us and our ability to run our own government in ways that make our lives better. TPP is about taking from We the People and giving to A Few People. It is a bad deal and it must be stopped.