Humans who spend time in space—specifically in microgravity—tend to end up suffering a wild menagerie of unexpected and unusual health problems.
How about Mars (1/3) gravity or the Moon? We know nothing about the medium-to-long term effects of way-less-than-Earth-gravity on our physiology. The most time anyone has spent under those conditions is a tad over three days. So nobody has much idea what the cumulative effects might be of life in Low-G. I suspect we’re going to learn that it’s a lot more complicated than we anticipate.
We’ve learned (and are still learning more) about the effects of medium-term microgravity on the human body, thanks to some 20 years of guinea pig humans living aboard the ISS. But we know next to nothing about effects of conditions somewhere between “zero”-G and full Earth gravity. We know nothing at all about the long-term (decadal/lifelong) effects of (say) 0.3G.
As for life in orbit in space-stations, we have some notion that we might simulate gravity by whirling things round and around at a speed that simulates gravitational acceleration, but will that be sufficiently similar to ‘proper’ gravity for our Earth-evolved bodies? Or will it turn out to be a hopelessly inadequate mockery for reasons we’re quite unable to guess? For example, in a whirling space-station (say) some dozens or hundreds of metres in diameter, there’s a rather substantial difference between the forces of ‘gravity’ experienced by our head vs our lower limbs… our heads being (presumably) quite a big fraction of the distance closer to the null-gravity centre of the whirling. Our circulatory system evolved in conditions where that difference is insignificant to the point of vanishment, but it may not like so much a simulation where there is a significant difference, resulting in pressure differentials in the various regions of the body that we were never meant to experience over longer spans of time. Not to mention associated coriolis forces…
So I suspect that living in space, or on Mars or the Moon, might turn out a wee bit more complex than we anticipate.