Argument: A Moonbase will help instruct establishing a base on Mars
Guy Gugliotta. "U.S. Planning Base on Moon To Prepare for Trip to Mars." Washington Post. March 26, 2006: "you have to learn how to do it, with real people," McKay said. "This is hard, but we can learn it. And if we do it right on the moon, we will be able to answer my ultimate question: Can Mars be habitable? I think the answer is 'yes.' "
Fraser Cain. "Why the Moon before Mars?" Universe Today. March 21st, 2005: "The Moon is a natural first step," explains Philip Metzger, a physicist at NASA Kennedy Space Center. "It's nearby. We can practice living, working and doing science there before taking longer and riskier trips to Mars." The Moon and Mars have a lot in common. The Moon has only one-sixth Earth's gravity; Mars has one-third. The Moon has no atmosphere; the Martian atmosphere is highly rarefied. The Moon can get very cold, as low as -240o C in shadows; Mars varies between -20o and -100o C.
Even more important, both planets are covered with silt-fine dust, called "regolith." The Moon's regolith was created by the ceaseless bombardment of micrometeorites, cosmic rays and particles of solar wind breaking down rocks for billions of years. Martian regolith resulted from the impacts of more massive meteorites and even asteroids, plus ages of daily erosion from water and wind. There are places on both worlds where the regolith is 10+ meters deep.
[...] Testing all this technology on the Moon, which is only 2 or 3 days away from Earth, is going to be much easier than testing it on Mars, six months away."