As the enormously successful Apollo program taught us, success is achieved by careful preparation - a grand challenge must be approached one cautious step at a time, to ensure confidence in the technology and to develop skills and experience in the engineers. It is wise to adopt the same philosophy with respect to the colonization of Mars. A careful, well-planned strategy for reaching the the new world is necessary, to minimize danger, and maximize both financial and scientific profitability.
Antarctica provides us with a unique opportunity to develop colonization technologies. The most apparent of these is that Antarctica is the coldest and dryest place on the Earth - it is an environment totally unsuited to humans. If we are able to demonstrate life-support strategies and technologies in Antarctica, we will be well prepared for developing those technologies required for survival on Luna and Mars.
Within the Mars community it is sometimes said: 'if you want to go to Mars, go to Mars', and that all this mucking about with Antarctica and the Moon should be avoided, but I think this is a dangerous philosophy. I understand that many people would like to see the fruits of their labour during their lifetime, in the form of humans on Mars, however this impatience is not really in the best interests of the astronauts whose lives are at risk. I agree that Mars is our destination, however Antartica and Luna provide us with golden opportunities to practice and develop our colonization technologies. An intelligent species would take advantage of these opportunities.
I expect that Luna will probably develop in a similar way to that of Antarctica since its discovery. There are several attributes of Luna that make it difficult to colonize - it has practically no atmosphere; high levels of radiation; a month-long day; enormous extremes of temperature; and only tiny deposits of water. It will be hard to live on the Moon - its inhabitants may have to spend most of their time underground to provide shielding from solar radiation; during the 2-week lunar night, they will live in artificial light; and food will have to be imported from Earth (maybe not always, but at least initially). Similar to Antarctica, Luna will probably be inhabited by a relatively small population, primarily used for scientific purposes (and possibly mining), and frequented by tourists.
Of course, Mars is also difficult to colonize, however, it has much greater potential. Mars has a tangible atmosphere, significant amounts of water, seasons, weather, and a day-night cycle very similar to Earth's. It is cold (average -60°C), and the atmosphere is very thin and largely composed of carbon dioxide, however, Mars can be terraformed (manipulated to be more like Earth), until eventually humans and other Earthly life forms can thrive out in the open on the Martian surface. Even if it proves extremely difficult to adapt Earthly life forms to the Martian climate, advances in genetic engineering will enable the creation of new organisms especially suited to Mars. Mars will one day teem with life - it is the new world.
Mars will develop in two distinct stages. The first stage will be adaptation - humans and Mars learning to live together in symbiosis. During this stage we'll develop our survival skills and technologies, effective terraforming processes, communications and transport infrastructures, societal systems, agriculture, materials science, and so on. Most of Mars' inhabitants during this time will probably be astronauts, scientists, engineers, and communicators, and they will live in enclosed, controlled environments with Earth-like air and temperature.
Mars is attractive and many people will still want to travel to Mars, even to live in enclosed environments, so there will probably be a steady stream of curious and adventurous souls from Earth during this period. The sol (Martian day) will eventually come, however, when the terraforming process has reached a critical point and a human can walk on the surface of Mars without the aid of technology. That sol will mark the beginning of a flood of humanity towards Mars, and thus also the beginning of large-scale interplanetary commerce and travel. It will be a new era for both Earth and Mars.
When this sol will be is a guess - it may take anywhere between 100 and 1000 years before a human can walk on the Martian surface unaided by technology - however, our current knowledge suggests that it is possible, and our imagination affirms that it is also worthwhile, regardless of how long it takes. The ALM strategy is aimed at this precise target.
The primary technology required for Mars habitation is environment control. On a planet whose temperature range is between -140°C and 20°C, and whose atmosphere is thin and comprised mainly of carbon dioxide, we must create little bubbles of Earth - enclosed self-contained environments with a comfortable 15-20°C and breathable air.