Why are we talking about colonizing other Mars, instead of building a bunch of huge space stations? Seems like the space stations are easier, cheaper, more scalable, and more flexible.
You could possibly find some savings by using materials on Mars to either build your colony or sustain it, and things like gravity which are expensive to produce in space are free.
Musk claims that it costs too much to move the mass required to build the space stations into space, but energy is actually quite cheap if you harvest it efficiently (solar), and anyway the cost of moving the mass is a amortized, so it's small relative to operational costs over time. It just seems to me that there are only two planets that we are likely to ever colonize, and one is already a wreck. Putting in an enormous amount of work to wreck the other just seems to put off the inevitable ... one way or the other.
