There is no reason almost all of the technology developed for a lunar base could not easily be adapted for a Mars base, and there is a lot to be said for help in an emergency being only a few days away instead of a few months when you are breaking in new technologies and new procedures. If you plan the transportation system carefully, even that could be adapted for Mars use. It isn't one or the other...it's a progression.

The key, of course, is the transportation. If you can move large amounts of material off the Earth and around in space, the technological barriers are a lot lower for a manned base effort. Note that the Space Station survives on regular resupply missions, not by recycling astronaut waste into food and water. There is no reason this procedure could not work for a lunar base, or with planning, even a Mars base.

Actually, I would not call it "colonization," but a base. Not for any stupid PC reason, but for accuracy. I think people moving off world permanently is a ways away. Even Antarctica has no permanent residents that I am aware of.

There are commercial applications for a lunar base, but not as many of them as Ferris implies. Solar power satellites work as well or better than lunar ones. Even if you make the materials on the Moon, it's still easier to ship them to geosynchronous orbit. Helium 3 is more or less a pipe dream. We can't even get a decent fusion reaction from isotopes that are much easier to fuse.

Tourism has great possibilities, and I could see it as a major moneymaker, but I wonder if you could make enough to pay all the base costs.

Then again, why not just make it a scientific and exploratory effort? How much money does the Hubble telescope make?

If one is going to grant the assumption that the government has a financial role in pure science, I see no reason that a lunar base could not be justified on this basis. The tourism income would be just a bonus.

Like most other industrial revolutions, it may be that the path into space is something that we can't now predict. Maybe tourism will be so hot that a Moon colony could be bootstrapped off of orbital tourism. Maybe someone will finally discover something immensely useful that can only be made in space. Who would have predicted where the computer revolution was going back in 1960?