Would the discovery of a planet seemingly very similar to our own at twenty light years’ distance from the earth be grounds for rejoicing because it is possible that intelligent living beings might exist there? Most definitely not. We must presume that there preceded the emergence of any such intelligent beings a long evolutionary prehistory of eating and being eaten. Intelligent beings replace this biological prehistory with real history which is hardly to be imagined, at least on planets not blessed with paradisical conditions of life, except as a history full of struggle and conflict.
Sure news of other inhabited planets, then, would be the occasion rather for the institution of a day of public mourning. This inasmuch as, up until the arrival of such news, we might have rested content in the assumption that our species, and its development of destructive forces, mass murders and wars, had, at least, remained, and would remain, restricted to a single planet and might thus have cherished the hope that all this would come to an end with us; but, after this point, we would face the certainly that this “us” would not, after all, be limited to our world alone.
 For more on this see Akerma, Das moralische Gesetz des bestirnten Himmels.