The most efficient way to colonize space is with self replicating robots/factories. Human settlement is probably going to be more of an afterthought, or along the lines of on-site repair and teleoperations personnel for the robots doing the heavy lifting. The concept of slave labor in orbital mining colonies doesn’t make much sense outside of science fiction.
Once a certain critical mass has been reached in terms of having systems that can convert raw space materials (asteroids, lunar regolith, and so on) to more useful configurations of their raw elements (metal, solar panels, breathable air, and so on) it will make more sense to set up habitats. These will probably be between planets, not on planets.
This will have some positive consequences and some negative where x-risk is concerned. On the negative side, access to high energy weapons is almost an inherent part of being in space, since it is relatively easy to create high velocity projectiles (gravity alone adds huge amounts of energy to any sizable object, including the sun’s gravity), and sterilizing the entire planet will be more plausible than even nuclear weaponry.
On the positive side, we will have decentralized our population and have the ability to survive if the earth itself is rendered uninhabitable. We will also likely develop more easily decentralized types of manufacturing tech which will protect against supply chain disruption, thus reducing economic paths of civilizational decline.
It is also worth noting that the earth’s carrying capacity can essentially be extended, guarding against overpopulation, by returning refined materials and/or energy from space, once the level of off-planet industrial growth hits a point where it becomes profitable to do so. So even from the perspective of people who want to stay on earth forever, there is incentive to develop this. You can also use it to guard against asteroid impacts, but that’s a relatively minor gain compared to the rest of the picture.
I’m with you on spinoffs argument, however we’re concerned with technologies of specific usefulness in space to tap space resources. What is the profitable application of a zero gravity refinery for turning heterogeneous rocks into aluminum? Assume the process is (at the small scale) around 5% as energy efficient as electrolyzing bauxite and requires a high vacuum. Chances are such a thing could be worth something in a world without cheaper ways to get aluminum, assuming you could work around the gravity difference. Not so much in a world with abundant bauxite, gravity, and an atmosphere. So there is little incentive to develop in that direction unless you are actually planning to use it in space, where it would be highly useful (because aluminum is so useful in the service of energy collection in space that 5% energy efficiency actually wouldn’t slow growth by much).
We actually do facilitate the replication of machinery, with the aid of human labor. An orbital factory wouldn’t have much time delay compared to the human nervous system, so the minimal requirement for a fully self replicating space swarm seems to be telerobotics sufficiently good to mimic the human hand well enough to perform maintenance and assembly tasks. No new advances in nanoengineering or artificial intelligence are needed. However, until such a system replicates itself adequately to return results, it would be a monetary sink rather than a source of profit. It would become profitable at some point, because the cheap on site energy, ready made vacuum, zero gravity, absence of atmosphere/weather, reduction of rent/crowding issues due to 3d construction, enhanced transport logistics between factories due to vacuum/zero gravity, etc, would all contribute to making it more efficient.