This is a linkpost to a 2020 review of a book about space colonization by a professor of political science at Johns Hopkins University in the Boston Review. According to the review, the book’s thesis is that "unfettered space expansion is likely to increase the threat of large-scale violence and generally exacerbate human insecurity". I'm quoting a few excerpts that might be most relevant to the readers of this forum. Bold is added by me. 

Dark Skies: Space Expansionism, Planetary Geopolitics, and the Ends of Humanity is a painstakingly researched, historically informed and theoretically sophisticated analysis centered on the disarmingly simple question: Is space colonization desirable? Deudney answers emphatically in the negative, in the process providing an invaluable history of Space Age dreams from the Enlightenment to the current interplanetary obsessions of libertarian plutocrats.

It is important to highlight the subtlety of this position, because it is too easy to dismiss all opponents of specific plans for space exploration, such as Mars colonization, as astro-Luddites. Like Clarke and Sagan, Deudney is anything but. He constructs a taxonomy of possible positions, with Promethean Technophilia at one extreme and Luddite Technophobia at the other. His own stance, Cautious Soterianism (named after Soteria, the Greek goddess of safety), gets between these extremes, favoring “decelerating” the race to space rather than abandoning it altogether. The goal Deudney urges is to “steer” the whole thing more prudently than is currently being done, an orientation that will result in numerous “regulatory restraints and even selective relinquishments” of some plans.

Deudney arrives at this insight by placing the drive to colonize the heavens in the larger context of the twentieth-century development of weapons of mass destruction as well as the efforts we have made—via bilateral and multilateral treaties and other legal regimes—to contain the threat they pose. The book’s thesis is that unfettered space expansion is likely to increase the threat of large-scale violence and generally exacerbate human insecurity. If we adopt this approach, Mars colonization should be shelved, for now at least, while we expand and enhance the terms of the Outer Space Treaty, an international agreement crafted in 1966 that places limits on various forms of space adventurism and militarization (for starters, nobody can own the moon).

In the beginning we went to space with the express mission of winning the Cold War and becoming more efficient at killing each other, a historical reality that tugs against the breathless visions of the technologists. In fact, this past looms over the whole subsequent project of space expansion. The quest to inhabit other worlds, Deudney suggests, has piggybacked on this darker purpose without ever fully coming to terms with it.

If this is right, we must look beyond the breezy pleadings of space expansion’s most ardent advocates and examine the actual arguments for this grand vision. There have been three broad patterns of attempted justification. The first appeals to evolution, the second to long-term human security, and the last to the expansion of human freedom.

The failure to grapple with this kind of scenario underlines what Deudney takes to be an entirely unexamined assumption of space expansionists: that “humanity will be succeeded by creatures who are significantly better than humans.” He calls this the ascensionist assumption, the notion that by going up we will inevitably become morally and politically better. So of course space colonists and their descendants pose no threat to us. Again, the point is not limited to space cowboys. Most techno-utopians—the giddier boosters of geoengineering, Artificial Superintelligence, nanotech, de-extinction, genetic enhancement, you name it—operate with some version of this background assumption. And that is putting the case charitably, because the other alternative is that they simply don’t care about the potentially catastrophic consequences of their dreams and schemes.

But evolutionary theory gives us no reason to endorse any version of the ascensionist assumption. It is obviously not the case that over 3.5 billion years of development, species—including Homo sapiens—have become appreciably more tolerant of each other. Life has always been, and remains, red in tooth and claw. In fact, while appealing to evolutionary arguments, space expansionists are covertly counting on the magical disappearance of this aspect of the evolutionary process. It appears that even as we bring life generously to space, we run the very significant risk of erasing our own future

That brings us, finally, to the other two attempted justifications for space expansion: that the program will safeguard the long-term future of our species and that it will enhance human freedom.

The association of space expansion with the preservation and expansion of individual freedom is probably extremely dubious. Space expansion, far from being a form of freedom insurance, is more likely to produce the perfection of despotism and the complete subordination of the individual to the collective. Those who value individual liberty should be strong skeptics and opponents of space expansion, not enthusiastic supporters.

Many space expansionists have expressed moving visions of scientific progress in lofty and inspiring rhetoric, but the uglier realities of nature and geopolitics have a way of hijacking good intentions.