I think you are conflating comparative advantage and absolute advantage. As the article explains, comparative advantage is what a country is good at doing, not how good it is compared to other countries. The latter is absolute advantage.
You can be worse than every country on earth at making X, but still have a comparative advantage in making it.
>And while I don't disagree that for some countries that are trying to move up in development, so-called 'sweat shops' can represent a stepping stone forward (2 generations ago, South Korea had plenty of them), the question is how long that's an acceptable excuse?
Understanding comparative advantage helps answer this question. Sweat shops should not be banned by the exporting country as long as it provides a comparative advantage to workers. That is to say, if sweat shops are better than the next best option, they should be allowed. Once better jobs exist for workers, sweatshops should be disallowed. Otherwise, banning them doesn't make replacement jobs, it just pushes workers into worse options.
Changes can also be made on the buyers side to not import products made in sweatshops. This could have positive or negative effects on workers in the exporting country. If the manufacturing country still has an absolute advantage in shirt making after the import ban on sweatshop goods, their people will be better off. If the absolute advantage now goes to another country, the workers will be worse off.