[edit: 2/3rds of this is probably strictly off-topic. But the post is hopefully long enough to confuse the mods.]
I agree that once you are out there going for volatiles it's perhaps marginally less to go for metals as well, and vice-versa. I do not agree that it's ever trivial to bring back large amounts of very heavy, dense material to Earth.
Not trivial, it just has to be profitable. Do that, and the process should ratchet, each step justifying investment in infrastructure and capacity that lowers the price of the next step.
Re: ISS. The material being bought back is prepared scientific samples. It needs to be protected, in some cases even refrigerated. It necessitates a re-entry capsule.
If there is large scale mining of high-value items, such as PGMs -- if that
business case ever closes -- then subsequent efforts to lower costs may be to shape the metal into a direct re-entry capable shape and coat it with slag from the mining as a heat-shield. (The PGMs "lithobrake", but at a reasonable terminal velocity to allow simple recovery of the metal.) Once that capacity exists, then the same method may also work on larger amounts of lower value metal like nickel.
Not having a parachute or other gentle recovery doesn't mean "asteroid impact", it's not binary. Recovery systems on capsules only cover the final few hundred km/h, the bulk of braking comes from the re-entry shape. A bubble of metal covered with an ablative heat-shield can reduce that terminal velocity to any arbitrary level. Trades will come from impact speed (risks plus recovery costs) vs processing costs to produce and coat the bubble.
And when people on this thread are talking about doing that for hundreds of thousands of tons of metal, that is not at all trivial.
Iron is cheap. So obviously it will be a long time before metallic iron from space is cheaper than mining and processing iron ore on Earth.
IMO, decades before it would ever compete with prices on Earth, there'll be earlier steps where it's cheaper to use asteroidal iron (and aluminium, etc) in "export replacement" for in-space uses. The point where it is cheaper than Earth-mining will spin-off from the existing in-situ use. (Ie, at some point, someone might be able to argue, "Cost of expanding production to meet projections of next 30yrs in-space use is $X billion, giving a unit price of $n/tonne. However, the cost of tripling the production rate is much less than $3X billion, giving a unit price much less than $n/tonne, that not only undercuts our rivals for in-space markets, increasing both revenues and profit margin per unit, but it even brings us within range of Earth prices...")
Finally - I'm not sure how your argument refutes my point that resource extraction is not a compelling rationale for exploration of space, at least given the current economics surrounding PGMs. It's certainly an enabling technology for exploration, and there may come a day when, if we're out there anyway for a different reason or set of reasons, it starts to make sense to bring stuff back.
It's the self-reinforcing aspect.
We clearly want to explore space. We spend a small fortune on it each year. Yet the cost of access and operations puts hard limits on what we can do. Demonstrated by the fact that multi-billion dollar space-rated (hence dumb, slow, limited) robotic systems are cheaper than sending an underpaid grad student with a trowel. Anything that significantly lowers the cost of accessing space will increase the number of people who can do the things they want. Anything that significantly lowers the cost of operating humans in space will increase the number of people who can do things they want personally
, on site.
And once you get to that level, it's obvious that people will do foolish and wasteful things, like tourism or even colonies, expanding the demand for volatiles (fuel, air, water), shielding, habitats, even food. That creates potential business cases for new industries, creating yet more activity...
Flipping it around. If lowering the price of access to
space brings the cost of PGMs within range of Earth prices, at production rates that don't crash the price too hard, then the infrastructure that is created to do so can be used for other things. (By "infrastructure", I'm including transport systems to/from the asteroid & Earth.) And
the mining operation itself becomes a market for other materials (such as fuel), which may help close the business case for volatile mining. Creating routine reusable transport to/from Earth means that you lower the price for many other activities in space (even if mostly unmanned). And lowering the price of fuel (hence the price of delta-v), lowers the cost of even manned activities in space. Which increases the market for other materials and products in space, which....
It doesn't matter what the entry point is, once we're in, we're in.
My personal opinion is that the case for PGMs doesn't close yet, even if New-Space lowers the launch prices. Cheap in-situ fuel must come first. The neat thing about that is that I strongly believe
the ices trapped at the lunar poles will be extremely scientifically valuable. So confirming the existence and studying the nature of that polar ice is of existing scientific value, without any regard for future commercial markets. You don't need to commercially justify a survey of lunar polar ice, it's just a scientific mission. (Likewise studying remnant comets in the inner solar system, to see if they are "dry" or just an insulating layer of carbon-materials over mixed ices. Any answer is scientifically valuable, and one specific answer might be commercially valuable in the future.)
But if someone actually can make money from mining PGMs, it simply makes volatile mining more viable, giving the volatile-miner a guaranteed anchor client. So I'm hardly going to be disappointed if PGM-advocates are right.
[Aside: Some people argue that if you lower the price of launch, you undermine the market for in-space fuel. However, IMO, by lowering the price of launch significantly, you expand the range of activities in space enough to increase the overall demand for in-situ fuel (and air/water). Look at SpaceX's Mars plans. Even ITS doesn't work if they had to bring their return fuel with them. A fully fuelled ITS-BFS in LEO is just capable of landing on the Moon and returning to Earth on a single tank; but it's vastly more capable if it lands on the Moon, refuels
, then returns to Earth. It's even more
capable if an ITS-tanker operating on the Moon is ferrying fuel to L1.]
[edit: some typos and ambiguous grammar]