To me, the best lesson that can be learned about sweatshops is that we, as humans, need to be protected against ourselves.
We are always going to search out the best product at the cheapest price. Sometimes we are just going to search out the cheapest product.
Sweatshops stand as evidence about our need for cheap products and how global regulations need to be in place to protect ourselves and those more vulnerable than the consumers of the Western World against our worst impulses.