Now this is where I have to disagree. "Wrecked" is very much an indisputable description for what micro-gravity does. There are health problems that develop even with short stints of micro gravity (less than a month) including abnormalities in the brain that we still don't know the long term health implications of. Keep in mind that the majority of people who have been sent up there are astronauts who are by necessity at a level of physical fitness that's not representative to the local population. For the average person, they will cope even less well.
If we want to establish a long term presence in space, we want to use rotating habitats to approximate the forces gravity places on the body. For these to not nauseate the human body, they need to be fairly large which is part of why there has not been any such stations built yet (another is scientists are obviously more interested in the effects of micro gravity than of something that already exists on Earth). Rocket launches are dropping in price sharply in recent years though and space tourism is likely to grow exponentially starting this year and out (there are already more civilian launches scheduled for this year than there has been since the space age started combined).
One question which we have no idea about is what are the effects of low gravity on the human body. There have only been 24 people who have visited the moon (only half of which walked on it's surface) and none of them stayed for longer than a few days. We don't know if the Moon's gravity is more than enough or if Venus's gravity would still too little. If the program does not burn into a fiery heap from a corrupt congress and Boeing, the hope is that the Artemis program may begin answering these questions.
> to not nauseate the human body, they need to be fairly large
I completely agree with your reasons why it hasn't been explored further (sadly budget issues killed even a small experimental module for the ISS[1]). Just how large is somewhat disputed though[2, pages 20-22]. By these estimates, ~10 Starship launches (ballpark $100M-500M launch price tag) could loft a dumbbell-shaped rotating station into LEO.
Hopefully the Gateway Foundation manages to get it's feet off the ground with it's starport idea. They are probably the closest I've seen any company to take these ideas beyond the conceptual stage.
Gravity is only part of the complex puzzle of our amazing cradle. There is also the microbiome, which we need to thrive long-term, small amounts of sunlight we can't do without, massive amounts of cosmic radiation, which will kill a human rather quick without a shield like the Earth's atmosphere and magnetosphere, the magnetic field itself, and probably other variables we haven't even discovered yet.
With space and robots we're very much in the situation "parents sending off their children to explore the world but unable to leave the village themselves."
Some of these concerns are valid (in particular the microbiome and the possibility and probability of unforeseen variables) but others are not.
Even assuming that we can't use mirror arrays to use natural lighting within habitats like O'Neil envisioned, there is nothing about sunlight that we cannot replicate with artificial lighting. In fact, we could make a safer substitute that forgoes the ultraviolet radiation.
It also doesn't take that much radiation shielding to do a better job of protecting us against cosmic radiation than the Earth does. While there is 100 KM of atmosphere between us and the vacuum, that is air and of a density that drops sharply with altitude. We could easily match and exceed that protection with plating of about 20 metres.
The reason why radiation is such a concern in space travel at the moment is because current launch costs prevents any but the most spartan kinds of shielding from being economically viable. Once we can construct launch assist devices like rotavators and orbital rings, that is not going to be a major limitation anymore.
If we want to establish a long term presence in space, we want to use rotating habitats to approximate the forces gravity places on the body. For these to not nauseate the human body, they need to be fairly large which is part of why there has not been any such stations built yet (another is scientists are obviously more interested in the effects of micro gravity than of something that already exists on Earth). Rocket launches are dropping in price sharply in recent years though and space tourism is likely to grow exponentially starting this year and out (there are already more civilian launches scheduled for this year than there has been since the space age started combined).
One question which we have no idea about is what are the effects of low gravity on the human body. There have only been 24 people who have visited the moon (only half of which walked on it's surface) and none of them stayed for longer than a few days. We don't know if the Moon's gravity is more than enough or if Venus's gravity would still too little. If the program does not burn into a fiery heap from a corrupt congress and Boeing, the hope is that the Artemis program may begin answering these questions.