I agree that the question isn't borders. If you are in Texas, northern Mexico is more "local" than NYC. But in either case, China is not local.
But you're arguing for placing pre-emptive barriers on what you think are "the right level of local". I'm saying, if you have open trade borders and price in the cost of externalities (like a carbon tax), then the market will work itself out in terms of where the "right level of local source" is.
The part that's never zero is called "structural unemployment", and was mentioned in the part that you cut. People between jobs, people who are moving, etc.
But unemployment-because-you-cant-find-a-job is not god-given, and in fact in various countries around the world there have been periods when this unemploymend was zero.
"the upcoming onslaught of automation" - the 60s called. They want their argument back.
I don't know if I buy that. Employment participation rates vary from decade to decade. They vary because people give up on finding a job, not because they don't want one. You may be right that those *with no choice but to have a job* (breadwinner for the family) parts of the population who are systemically unemployed can reach 0, but that's not full employment. Moreover, it's not consistent. You're always going to have periods lasting as long as a decade where some giant shift (such as globalization, or automation) will wipe out entire job sectors. So even if your argument is "those jobs will eventually be replaced", you need *some* solution to the decade-long vacuum those things created. And I don't think impeding progress Luddite-style is the answer. Nor do I think impeding progress "anti-trade" style is the answer either. It's more economically efficient during those times to do something like UBI.
How we are all caught in the Silicon Valley mantra and the Venture Capitalist religion. Most of the really large and powerful companies in the world are not called Google and Facebook. They are energy companies, food companies, and a dozen others. Trade and technology matter, but you buy an iPhone every year while you buy food every day.
This isn't a Silicon Valley idea. Notice I didn't just say tech, I said tech and trade. This is well established amongst economist. All those energy, food, etc. companies are the "trade" part; they find ways to distribute resources more efficiently. Do this simple mental experiment: what if every city was to produce their own crops of every type instead of importing/exporting from other areas? Would that be more or less efficient? Expand that idea to a global scale and you have your answer to why shipping from China or Brazil for certain things can be better.