Whenever I watch a Discovery Channel program discussing the possibility of a permanent Terran colony on Mars, I always go nuts! Why? Because there are a number of very good reasons that Mars is presently classified as a "dead planet" (excluding possible deep soil extremeophile bacteria or other simple life forms, of course).
Yes, I'm aware that we already know how to warm up a planet using greenhouse gases like methane, carbon dioxide etc. Of course, such a process would require a century or two and the expenditure of trillions of dollars (at $10,000+ a pound) to heat up the Red Planet. However, even an artificially warmed Mars is still a DEATH TRAP for at least two of the following reasons:
1. Mars has no magnetosphere because the core cooled billions of year ago. As a result, the poor world lost it's atmosphere in the distant past due to repeated solar storms, CME's (Coronal Mass Ejections), etc. A colony on Mars would have to frequently retreat to deep underground caverns to be protected from solar storms and the accompanying radiation. In addition, the terraforming process would never really ever be done as the atmosphere would be continually venting into space on a regular basis during solar events. To me, it's like filling a balloon with a hole in it, or bailing a lifeboat with a gash in the keel. Visiting astronauts could handle solar storms with the proper preparation, vigilance, and Earth-based assistance. On the other hand, a major CME impacting upon a human civilization on unprotected Mars would be disastrous.
2. Mars does not have a large moon to help stabilize it's axial tilt as the lucky Earth does. Over millions of years the axis of Mars shifts chaotically. Any long term colonization effort would certainly be catastrophically effected by the unpredictable axial movements. Imagine the mega tsunamis, earthquakes, windstorms, weather changes etc., that a warm, wet Mars would suffer in a 45 degree axial shift! Just a fraction of that shift here on Earth would most certainly be enough to obliterate our existing human society, if not the entire race. Short-term scientific bases could certainly afford to ignore this remote hazard, but not a long-term permanent Terran colony. Indeed, a Martian colony purported by people like Dr. Chris McKay to be our ultimate species diversification effort could not afford to overlook such a serious hazard!
The unfortunate reality is simple. Mars is merely the best of the three very unsuitable inner solar system planets, currently within our range of technology. Bankrupting the Earth, however, to plant a permanent Terran civilization on Mars is like forcing yourself to chose the best-looking woman at a single's party for never married woman in their 50's and 60's. It's not going to be pretty no matter who (or what) you select! Personally, my advice would be to stay single and wait for a better opportunity.
I'm all for the exploration of space. However, we need to understand that the Earth is the creator and the ultimate custodial parent of our race for the conceivable present and future. We can visit with manned craft our fellow worlds like Mercury, Venus, and Mars if we have the will, but we'll always be only unexpected guests dropping by to say a quick hello. Of course our technology is quickly developing, but how advanced will we have to become to create an entire planetary magnetic field and fabricate a Moon-sized body in the proper orbit? Unfortunately, there just is no realistic second home within our solar system.
Until the development of a Star Trek level of cheap, faster-than-light travel or other similar sci-fi high tech advance that can take us to other stellar systems, our race is stuck on this blue-green ball. We need to focus on the business of staying alive here for the long haul, rather than looking for ways to skip out on the mess we've created.