Cost-effectiveness must include the realization that their American purchase supports more domestic economic activity through the multiplier effect. That effect is not present when you make no domestic purchases and your (or your children's) taxes will ultimately increase to make up for the loss of taxable economic activity.
Also cost-effectiveness can't include convenience. A consumer's time is not so valuable that he must go to one giant store to buy everything made in China. If they do that (e.g. spur of the moment Walmart TV purchase) they end up with low quality items which negate any savings.
Yeah. That's why Wal-Mart's the largest retailer on the face of the earth: they sell nothing but cheap junk.
Never mind that they sell the same thing Target, and Costco, and other retailers sell. They just sell it for less.
In your world, American consumers are all stupid, and getting taken to the cleaners by Wal-Mart.