Adding more resources doesn't solve the problem that they aren't being managed sustainably. We can't exhaust all the resources in space, but we could definitely exhaust all of the resources accessible to us in space. Like how we can't exhaust all of the oil or all of the gold on this planet, but we could exhaust all of the resource which can be mined economically.
This was once explained to me with a metaphor of a bacteria colony in a jar. The colony doubles every 24 hours. So they quickly exhaust the space in the jar. No problem, you give them another jar. 24 hours later, their population doubles, and they have filled both jars.
Resource intensity of GDP has been falling for decades, most quickly in developed economies. Space-based resource extraction isn’t going to be radically cheaper (if it ever is cheaper) than terrestrial sources with known propulsion, so that balance is unlikely to shift. Herego, replacing terrestrial extraction with moderately-cheaper space-based extraction would reduce harm to our ecosystem without changing our economies to turbo-consume materials and thereby accelerate terrestrial extraction.
I agree it may reduce harm (depending on how the actual costs shake out), but the calculus remains that if you have access to finite resources but your needs are expanding exponentially, and you are not recycling them in some way, you will run out of resources no matter how many you have.
I'm not opposed to exploiting resources in space, I think we should pursue the goal of being an "interplanetary species", but I think it's important to understand that it isn't a silver bullet or a free lunch. We still have to change our economy to be more sustainable.
Not to mention that it is not clear that exploiting space resources or becoming interplanetary is possible. I presume that it is. But we shouldn't bank our future on something unproven. We don't know if we're a decade away from mining our first asteroid or a century. We should assume that our future is here on Earth with the resources currently available to us, until proven otherwise.
> if you have access to finite resources but your needs are expanding exponentially
Our material needs in many categories are not expanding exponentially. On a per-capita basis, in advanced economies, it's been flat in several categories.
If anything, the constraints of spacefaring seem perfect for nudging a culture and economy towards conservation and recycling. Building lunar and Martian colonies requires short-term sustainability in a way that does not have clean parallels on Earth.
> we shouldn't bank our future on something unproven
Nobody is banking on space-based resource extraction.
> We should assume that our future is here on Earth with the resources currently available to us, until proven otherwise
Bit of a paradox to this. On one hand, sure. On the other hand, given two civilisations, one which assumes space-based resource extraction and one which does not, which do you think is going to get there first?
That sort of thinking needs to first and almost-entirely be directed at China, India and Africa, then we can talk about sustainability and what the West can do.
This was once explained to me with a metaphor of a bacteria colony in a jar. The colony doubles every 24 hours. So they quickly exhaust the space in the jar. No problem, you give them another jar. 24 hours later, their population doubles, and they have filled both jars.