[CapitalistCartr]

I do not understand the obsession for focusing on colonizing only planets. We won't be viably "in" space until we produce mass quantities of raw materials from The Moon and asteroids. Lifting from Earth is always more expensive in energy. Once we build space stations, why would people who grew up in them want to live "dirtside"? Why would people who grew up on Earth want to live on Mars instead of a nice climate controlled habitat? I'm sure some will, but I bet most won't. Beyond mining and tourism, I doubt Mars will be heavily populated.

[lmm]

To survive long-term without getting massively irradiated you need, at a minimum, metres of rock between you and the sun (and as you say, lifting them from Earth is going to be expensive). Ideally a magnetosphere too. Gravity is also desirable for health reasons and random practicality things (e.g. in zero-g you have to sleep in a draught, as otherwise there's a risk of a dangerous bubble of CO2 forming around your head). And temperature can be a huge problem for spacecraft that aren't attached to a big heat reservoir - scorching in the sun, freezing in the shade.

Maybe ultimately we'll be able to construct nice habitats for orbiting stations, but with current engineering capabilities rocky bodies are the only safe places to stay long-term. I certainly expect we'll get to asteroids eventually. But for now, Mars is closer than the asteroids, closer in delta-V terms than the Moon, and much more promising in terms of having organic-y raw materials available for farming and fuel. It makes sense to go there (or maybe Venus, but aerostats would be a big chunk of new engineering) first.

[27182818284]

It isn't an either or.

Colonizing planets and producing space stations would only help enhance the technology, provide refueling and repair places, and much, much more. People will have preferences on where they want to live (dirtside or not) in the same way people have preferences on where they live now. I think it would be safe to assume there would be a little of both (spaceside and dirtside) living out there. (I think that resource-wise, there will be more on planets because of its benefits)