My question is as follows - let's assume our objective function is to have as many humans as possible living outside the confines of the Earth as soon as possible. For this, we need to provide those humans with some habitat outside Earth. One approach is to try and colonize other bodies in the solar system like Mars. Another is to build our own habitats, starting with the vicinity of Earth. Which of the two approaches will get us further in terms of the stated objective function if we start investing resources into one or the other now?
There is talk of inhabiting Mars and making life multi-planetary. I personally think the Moon is a better bet, but another approach is to simply start expanding the International Space Station so it can support more and more people. Then, we can simply build more of those. These large ships would start to collect more and more energy from the Sun, which is going towards a Dyson swarm. The question is, why even bother going to Mars and inhabiting it as opposed to just disassembling it for material when the time comes? Is it substantially easier to build a life-sustaining habitat on Mars than an independent spaceship?
The advantages Mars might have are that it has a lot of rock under which a human colony can get shelter from incoming radiation. Also, it has some gravity which we humans are accustomed to (though just a third of Earth).
The advantages of the space-station approach is that you can stay close to Earth. This is valuable in terms of being able to get supplies there much faster, help arrives quickly in case of emergencies, the close contact ensures much less psychological hardship for the inhabitants who can always go back to the planet for visits, do Skype calls with relatives, etc. You can also stay within the Van-Allen's belt so you don't need too much extra shielding, at least in the initial phases. Also, for intermediate economic motivation, this ever-expanding space station could start as being an exotic hotel for the wealthy.
So, if our goal is to have our species acquire a substantial footprint outside the Earth, should we invest our resources in going to Mars or the Moon and set up shop there or simply start expanding the space station to the point of a city and then rinse and repeat? To me, the latter option seems much more logical but am interested in alternate opinions.