As I see it, we have had decades of experience with both free trade and import tariffs so we have enough information now to make an informed decision about which way is better.
We are talking about the manufacturing of goods here, and all those processing steps of mining materials, smelting, fabrication, packaging, marketing and sales. Each of those steps are laden with jobs. If you move manufacturing offshore, the jobs go with it, but you benefit by having cheaper goods. However, if the jobs go, how do domestic workers earn a living? Which leads to the second unintended consequence – balance of trade deficit. A country that just buys foreign goods and sells nothing in return just racks up a huge debt.