Just because people collaborate from all over the planet to make the pencil, doesn't mean that's the way it has to be. This kind of collaboration simply enables economics of scale to kick in (and possibly improve quality as well).
I agree. I think smaller cycles of dependency are possible (and for the sake of stability maybe better). But we probably have to figure that out, before we go to mars ...
Sure, but it does show how speculative Musk's plan for a "self-sustaining city" is. There is no such city on Earth. What makes him think it would work on mars?
Then scale back from 100% self supporting and make a place on mars that is most self-supporting or self-supporting in an emergency. They don't need to be self sufficient from day 1, they need need to be self sufficient enough to eventually get by without constant injection of resources. At some point that can be part of this economy that makes it unprofitable to have self-sufficiency on Earth, but because of trade costs the economics will look different, but not impossible. Locally source will be 1% the cost so buying from Earth with done only for the most valuable items. Things like seeds or IP make perfect sense to buy across the gulf of space. Thing like bulk lumber and toilet paper do not and probably never will.