Technology

The most not caveat is we don’t know how much gravity is how necessary. We know that microgravity in orbit is too little and not really sustainable. Is gravity on the moon enough more for long term health? Is that on Mars? That’s just two of the questions we can’t know until we get there

So you build spinning space stations instead of settlements on the martian or lunar surface. Likely close to the same material cost, if not cheaper, while allowing us to actually choose the amount of gravity to generate. We don't know if martian or lunar gravity would even be sufficient to avoid negative health affects.

Settlers routinely sacrifice their health to be part of the first wave of people to stake a claim on fresh territories, considering how insane that got during more or less every colonization effort in past history I strongly doubt that harming human health will be a barrier to the whole thing, for better or worse. (I think mostly for worse tbqh, but I still see it happening unless climate change ruins everything, or nuclear war, etc)

Yeah, but the point is that if you want the real-world equivalent to the habitable worlds opened up by the protomolecule as regards Mars, that's actually just the entire rest of the outer solar system, especially the moons and asteroid belt. They're exactly as habitable as Mars will ever be in actual reality. Mars stops mattering except as an orbital pitstop as soon as there are places that are just as good if not better developed farther out, in smaller or non-existent gravity wells.

Mars has no active geology, therefore no Van Allen belts, therefore the only shielding you get is if you bury yourself. And to generate the energy required to artificially generate Van Allen belts that can actually protect us from cosmic rays... first, it's a preposterous amount, second, it's energy rent you have to pay in perpetuity to get an inferior environment anyways and zero resources that aren't available in greater abundance in cheaper gravity wells, because you're not realistically going to be spinning up the core anytime soon. Then you need to initiate planetary-wide processes to erode the toxic regolith. The numbers just do not add up.

Then there's the 38% Earth gravity, which A - is likely to be as unhealthy as a spun-up semi-microgravity environment B - isn't strong enough to retain any atmosphere thick enough to support humans, which means not only do you have to pay a continuous gargantuan energy rent just to one day walk on the surface without being killed by cosmic rays, you also have to import atmosphere which you're guaranteed to have to replace.

I enjoy the Expanse, but in spite of its hard science reputation it's honestly about as realistic as Star Trek in a lot of ways. Terraforming Mars is a fun thought experiment but Jules Verne level out of date at this point. Take it as an unrealistic backdrop for a very fun geopolitical space drama, not a realistic exploration of how space development would actually go. They needed a third power to make the politics complicated. Nobody's ever gonna breathe the free air of Mars, that's a fantasy, and that's knowable today, which means it'll never be invested in seriously.

The gravity problem is also best solved away from the surface of any celestial bodies. Massive spinning space stations would be much more pleasant to live in in almost every way. Unless a planet or moon has a good reason to land on it (e.g. material to be mined) it makes much more sense to simply build a habitat away from the gravity well and build smaller work camps on the surface that can be supported by the main habitat(s).