THE MOST PROFITABLE, and perhaps most dangerous, factory in the United States is a two-story, off-white block about 20 minutes north of central Fort Worth, Texas. It resembles many of the other buildings in a rather barren suburb along US 287, and, had there not been a large sign inviting passersby to visit, I would have driven past without a sideways glance.
Inside, it looked no more remarkable. A man in a Carhartt T-shirt and baseball cap walked slowly across the patched concrete floor; a woman with a blond ponytail in a black scrunchie jacked up a pallet; union T-shirts bearing the word “Solidarity” were the most common item of clothing. There was an unfamiliar smell: Imagine a new car filled with the hot air from a vacuum cleaner.
A half-dozen or so of us visitors looked down
