Protectionists would have you believe that domestic firms would be helpless against those viciously efficient foreigners, so we must have trade barriers to stop that pressure. But it’s actually that competition from viciously efficient competitors which drives up productivity and thus increases living standards. If domestic productivity is low, or lower than foreign, that is exactly the reason not to put up protective barriers. It’s only under outside pressure that our own producers up their game.
If domestic productivity is not lower than global then of course there’s no argument at all for protection. Who needs tariffs against less efficient competitors? Reading the runes of trade correctly insists, either way and whatever the state of the domestic economy, that we don’t want to have restrictions upon the very thing which makes us richer.