"Sometimes I think we are alone, sometimes I don't. Either way the the thought is staggering"
The presence of extraterrestrials in the popular imagination is a testament to the plasticity of the human imagination. One could argue that fictional ETs are simply reworking myths of angels and demons. Alternatively one can say they are essentially new myth - one that is elementally modern (similar, perhaps, to narratives of Artificial Intelligence battling their human creators). Either way stories of civilizations in space composed of human looking creatures (with prosthetic foreheads to make them look a tad different) or bags of protoplasm form a staple of our culture's stable of possible futures. All this without a single shred of evidence that they exist.
Stories matter. Stories are how we understand ourselves and set our individual and collective life into context, creating meaning, establishing purpose and building relationship. At the highest level our collective narratives rise to the level Myth. As Joesph Campbell, Mirce Eliade and others have stressed our dependence on Myth have never gone away in our march to modernism. It just went underground reappearing in "that fantasy factory" (as Eliade called it) of movies and novels. In this sense it is important to pay close attention to both the science and fiction of SETI as well as astrobiology. And, in this sense, the introduction of sustainability issues into astrobiological thinking marks a turning point, a maturation perhaps, in our thinking.
Beyond the infinite futures of Star Trek, beyond the dystopia of the Terminator, beyond the easy optimism or quick despair we awaken to what might be universal for technological societies - limits and their consequences. We still don't know what sustainability means. We have no examples of technological societies that are sustainable over long timescales (is it even possible?). All of these questions however will be solved first in the imagination for that is where all creativity begins. Our first steps into thinking about sustainability, SETI and astrobiology represent an opening of the imagination.