Take the idea of Mars settlement and use it as a model for life on Earth.
Consider that Mars is a waste, not a promised land, not a resource but a source of struggle - one which can be found on Earth, may not for all, but for one. Thus, the new world is not only there, but anywhere Mars rises in the sky.
Consider that this new world is where one decides or has to live independently from Earth's biosphere. A new environment, as-if the desert of Mars, comes and gives rise to new demands - tools, crafts, foods and materials, such which are unreasonable in the heavens of Earth.
Consider that the outward extension of humanity and Earth's life in large can be copied inward to the borders of nations. In this view, space colonization is not just indirectly causing benefits, it's a continuation and exemplification of the same effort which is possible here and now. What is beyond Earth a necessity, here it is a different culture, a different game of life.
Consider that the land of Mars is meaningless - no ancient text spoke about it, no nation binds its destiny to it, but this emptiness and opposition allows human will to grow - without clashing with another. It is a new constitution written to the indifference of the Waste, it holds a new universal right to leave producing new economies, the new individual possibilities thus crystallize to new structures - enabling in the effect those individual options.
Consider that this new Border facing the Waste is not merging or dividing any us and them, nor good or bad, but it's built on the distinction between the world and I. And the Waste is enemy to all and ally to none, success of anyone or one nation shall be of all. It is the external and universal enemy to all and one, to all humans and living beings. It's the place which is thus in life experienced as an event of closure, of limitation.
Consider that to live on Mars won't be just an adventure, a business or propaganda, one does not just explore rocks and dust, but a new form of life. As with inventions of the novel, theater, market or laboratory, new scene, a new place, a new medium is opened to see self and the other differently. The price of achieving Mars is this new medium, a new frame, as-if currency to pay for what is unpaid for, as-if new language to say what is unspoken, to have power to say things differently, to break from established monologues, to have something different to point out. Its empowerment and this power comes not from a book, or history, nor reason or compassion, this power comes from its might against Mars.
Leaving Earth is unreasonable because it's an act in a different world of reason and meaning. However, consider then that it has to be judged as whole, understood and described as totality and then the reason for this thing to the world and humanity. The extension It is as-if a new organ, a new world machine, of human species - what function does it serve?
Consider this answer - it functions as history. It's a new theater of humanity, observations of great deeds and efforts, lectures on failure and success. The distance of space and extreme conditions can serve as the well of the past. It does not erase current history, but it breaks the pattern of wars and therefore, the expectations of wars. We can look back and look at the history of those living in the middle, facing the Waste, living on the Border. The spectacle of Mars colonization is uncovering what is true and always has been - that life is a struggle, cities and man-made environments evelevated this struggle to competitions at best, wars at worst. Next step is to remove the mediators - on Mars face the world as species, on Earth as one. Different scales, similar difficulty; same horizon - the final one.
This all comes to a promise - that we are at reach to a solution of the paradox of war and peace. Till this moment, all those who speak for world peace, would have acted on such a premise, would only cause a war. And we are not at world war only because of the nature of war not of peace. The war is Waste, it spreads in peace and there are no defences to it. The solution is to be in perpetual war against the world - to move from heaves of Earth and to face dessert, to build structures where anyone can leave for, or use inside of nations.
To leave the paralyzing paradox, a new dimension is needed, an option to act differently. Defence against both war and peace, a reason and practice instead of fear of war or hope for peace. It's not an abundance or harmony as conditions for peace, but distributed power to leave - gravity of Earth or society. The defence is the outward and inward Border - both additions, new pages in atlas, for few to hold the defence, constructed by leaving.
The good news is that physical reality, the solar system and Earth as it is - or to the limits we know it, enables us to produce new observational situations and produce more knowledge about self. Similarly, observatories are built by changing the world to see more of it, to see more of humanity, many have to move and do more. Not higher towers, but humans in further distance.
And on Mars - Moon or beyond, its truth shall be in its might against the Waste. No new ethics and ideas are necessary, but more things to do. THere is not true knowledge to establish unity and peace, it's not a quest of reduction and elimination of truths, but a mission to build more, to move more, to be more independent - but not centers of world, in cities and structures built by others.
Thus, finally, consider that extending Earth's ecosystem and human species has a direct connection to the state of humanity and nature on Earth - if it's observable, it happens here, the Earth rises as a star on Mars - and this again is seen on Earth’s sky. The promise is that through that those against war can act now - the manifesto of this movement is the act of leaving Earth, to body and creating structures and tools to live independently from the economies of Earth.