Preface: This is not a good argument for why astronomy is important now. But it may be in the future. Earth is a limited habitat. Bacteria in a petri dish show the same growth curve as humanity: exponential growth. An exponential curve grows very quickly, but we are in a finite (non-growing) environment. If humanity is to continue its growth, we must find new worlds to inhabit. There is always a moral question of whether we should continue our growth and attempt to conquer significant portions of the galaxy, but we probably won't (and maybe shouldn't) start examining the morality of our survival until it's ensured. Consider what happens if humanity stops growing. Our current economic system is completely dependent on continued growth. The financial markets can't survive unless more wealth is constantly being generated. Interesting calculation to try: Divide the total solar energy input to Earth by the average energy consumed per person, or the minimum energy (theoretically) per person. It's probably not as large as you think when you take into account efficiency factors.