"Without something new to discover, to tame, and to colonize the human spirit will suffer."
Support? Document? Explain, fer cryin' out loud. And who cares? Aren't there better reasons for colonizing space?
Justify the rush. Explain your urgency. Concrete rationale, please, not post-Star Trek frontierism.
Is it because you want a challenge? Figure out how to get people to burn less fuel and have fewer babies. Figure out how to get the people here now to manage the resources they have. Unsexy? Sure. Boring? Often. But so's colonization, read some American history. And here's the clincher: we have to solve these problems anyway, whether we solve them here on Earth or somewhere else.
Speaking of history, why is it such a disaster that we have passed THIRTY WHOLE YEARS between landing on the moon and living on Mars? How much time passed between European discovery of America and permanent colonization there? And how much space do we have to cross this time, versus last time? And how much adapting will we have to do this time versus last time? Part of the reason why so little has come of the lunar landings is the simple fact that they were conducted, in large part, to be able to say "We done it!" rather than looking beyond that goal and asking "what next?"
Sooner or later, even under the best possible conditions, we will use up this planet or it will just die out from under us. We know that's going to happen, so we might as well prepare for it sooner rather than later. That still doesn't excuse the cowboy enthusiasm for a headlong rush to Martian colonization, for a number of reasons.
Read Asimov's late-life writings on this subject. Is Mars going to be our last stop? I sure hope not, it's a cold, boring rock of a planet and if terraforming is even possible there it'll be a long way off. I'd also prefer not to repeat some of the planning boo-boos that have made our cities here on Earth such dreadful places for so many people. So let's do this in a calm, rational, planful way for once. Rather than repeating the North American land rush of the eighteenth and nineteenth centuries, for no reason other than "the land's out there and nothing that looks like me lives there now," why don't we expand in a way that we can sustain? Take SMALL steps. It's less risky, less expensive (financially and ecologically), and we have the time, for now.
Go to the moon first. Permanent colonization of the moon will require solving a lot of problems that we'll face on Mars. It will be easier and cheaper -- just the expense of launching all the raw materials we'll need to get started will be greatly diminished if the target is the moon. And it will provide an excellent stopping-off point on the way to Mars. Why aren't we living on Mars yet? Why haven't we even set foot there? Because it's damned far off, and consequently really damned tough to get there. We know we can get people to and from the moon. If we can't get a colony on the moon to support itself and to generate a raw materials surplus, then chances are we won't be able to do it on Mars either and there's no justification for all the effort in any case. If we're going to fail, best to fail cheap and close to home. We might even get a second chance that way.
If we can establish a permanent, lucrative foothold on the moon, our opportunities for expanding past Mars become much more attainable.
ISS is an excellent step in the right direction. It is justifiable based on terrestrial concerns alone (better drugs, better raw materials). It is a step toward colonization (zero-grav manufacturing, hard vacuum survival, one step up out of Earth's crippling gravity well).
Leaving this planet is necessary for our species' survival in the long term. But our methods and and timing should be carefully planned as an open-ended affair, not an overenthusiastic fling toward one closed-end goal, be it Mars, the moon, or Alpha Proxima. If we don't learn how to survive in space in general, rather than Mars in particular, we're doomed sooner or later. And we're many incremental steps away from that goal. We don't even have fusion figured out yet, and we're going to need it. We're also kidding ourselves if we think that "humans" as we know them now are the ideal life form to handle space colonization, and this species is a LONG way off from being willing to accept a redifinition of what it means to be a human being, so far off it makes fusion, Mars, or any other concrete goal seem small by comparison. Why launch all this bone and muscle, all this water, into a realm where bone and muscle just aren't the best tools for getting the job done?
So please, let's not burn our planet and our species to a cinder just so that you can have a winter cottage on Mars. That's not what this is about. We either transcend planets, this and any other, or we wall ourselves into a dead end. If we expend too much getting to Mars, we may lose the chance to get past Mars.