A reason to go to Mars

I find it interesting that 0.1% of Phobos could build ten
Island Threes. That's enough to house one hundred million
people in comfort, and at any gravity level from zero-G to
one G (including Martian gravity, if desired).

So a full percent of Phobos would be enough to house a
billion. Seven percent and you've got room for more
people to live in comfort and affluence than currently
live on Earth, in conditions ranging from squalor to
splendor. Seven hundred Island Threes, at any gravity.

OK Mars advocates, how long until there are one hundred
million (or a billion, or seven billion) people on the
surface of Mars?

My story (the one with Anzu) mentions Mars.
"Plenty of people have been born on Mars. Nearly a
hundred thousand people live on that planet, and several
times that many in orbit about it."

Of course, I've got some ideas for those moons, too. In
fact, Martians should like my Martian moons idea. Next.