I don't get it. Instead of a truck driving 100 miles from the factory to the store, you now have ships driving thousands of miles halfway across the world to a port, where a truck then picks up the product and drives 100 miles to the store.
The USA loves to brag about how bad it was in the 70s - remember the TV adverts with the Native American and a tear in his eye? - and how well we cleaned up our act. Lol. Ohhellno. When we offshored the manufacturing, the associated pollution when with it. We didn't clean up as much as we outsourced our pollution.
Point being, when we see the photos of Beijing and the smog, that's not China's smog, we, and the rest of The West "owns" a good chunk of that smog. But the politicians and the corporate leaders aren't going to be transparent about it.
Do the math... Of course shipping costs may have changed, but parents' point stands:
The energy consumption (and labour costs) embodied in many products' fabrication, is much higher than energy consumed to ship 'em around the world. And thus those products will be fabricated where it's cheapest and/or most efficient.