"By the time such things could be financed, resourced, designed, built and exhaustively tested whatever population, resource and climate issues are threatening will already be well in train. Too little, too late, and unrealised tech."
American money, resources, engineering designs are in place NOW.
The money is spent poorly.
The designs (for tested technoligies) are undeveloped.
The resources are frittered.
All cuz of a lack of will.
Whatever the reason, it ain't happening. There's already MANY people who are against space programs, seeing them as a waste of money. I disagree with that, but it's a common view that restricts space progress.
"Then think about how many people you could take."
I'm not sayin' we should be ark-buildin'. There's no need to radically de-populate the Earth. I'm sayin' we need to frontier-explore. Earth is 'small & crowed' only perceptually, but that's enough to make us into scrabbly rats. We need 'room', we have 'room': look up.
It's not hospitable. Look over at all that ocean - not great for living on either unless you love being squashed up.
"A structure large enough to house massive human populations plus nature - trees, mountains, rivers, animal ecosystems, wind, rain, clouds etc - would surely start collapsing under its own gravity."
https://www.popularmechanics.com/space/ ... -17268252/
...and on and on and on...
We have the proven technologies and engineering, we have the resources, we have the stepping stone (the ISS): we just need to pull our heads from our keisters and continue what we started.
Quoting from one of your links:
The total land area inside a pair of cylinders is about 500 square miles and can house several million people.
That is exactly my point - it sounds like a ghastly way to "live", about survival rather than thrival.
Interesting links, though. Thanks.