Big Al if you change your market from parochial to global then the only mechanism to protect home markets is tariffs. Tariffs increase the prices of imported goods. Because of this, domestic producers are not forced to reduce their prices from increased competition, and domestic consumers are left paying higher prices as a result.
How this pans out in terms of sweatshops versus ethical purchasing is a moral question not economic. Thus far the only product that springs to mind where the question is answered on the wrapper (to give consumers a free choice) is fair trade coffee. It is a sound business decision to locate to lowest cost base, but the jobs lost at point A are gained in new location B. The UK is the 5th largest economy in the world. Theoretically jobs lost in one sector should be readily replaced in another(depending upon where we may be in the economic cycle)
Another factor to bear in mind is that certain industries, that are now virtually defunct, were very dangerous. Fishing and to a lesser extent mining killed hundreds. This cannot be said for cityworkers,