Because you handwave with handpicked examples, not prove a general principle.
We can actually do a pretty simple test right here on FreeRepublic, by asking how many people on this board work in an industry in which they: 1) produce things that are made entirely in the U.S., from parts and/or raw materials that are supplied by U.S. sources; and 2) can afford to purchase the items they produce without incurring any serious financial hardship.
I'm willing to bet that the answer is going to be almost zero -- and anyone who can meet these conditions would then have to undergo a second level of scrutiny related to Point #1: Can everyone who works for the U.S. suppliers also purchase the end-product they are producing?