As I see it, the real question for space colonization is "How small of a population can be 100% self-sufficient in manufacturing?" and the smaller that number is the more likely it can be successful. If N=1, the odds are great, if N=10,000,000 it will not succeed.
The basic problem is that you can't export anything from Mars to Earth that makes Mars colonization profitable from a Terrestrial perspective -- so at any time the flow of resources could be cut off, see the Asimov classic story
The Muskian model that we're just going to send millions of people canned food makes no sense at all.
Eric Drexler's molecular assembler program has foundered but we need something functionally equivalent, living things pull off basically the same trick, maximizing what we can do with them is an obvious path to "advanced manufacturing" together with flow chemistry, 3-d printing and other methods.
The basic problem is that you can't export anything from Mars to Earth that makes Mars colonization profitable from a Terrestrial perspective -- so at any time the flow of resources could be cut off, see the Asimov classic story
https://en.wikipedia.org/wiki/The_Martian_Way
The Muskian model that we're just going to send millions of people canned food makes no sense at all.
Eric Drexler's molecular assembler program has foundered but we need something functionally equivalent, living things pull off basically the same trick, maximizing what we can do with them is an obvious path to "advanced manufacturing" together with flow chemistry, 3-d printing and other methods.