The main argument against spending money in any sort of space program is that there are a lot of needs to be fulfilled first on Earth, covering a broad scope of things, from famine and poverty to financial woes and political considerations, but is this a case of first having to break eggs to make an omelette or not?
what would happen just in the areas we have mentioned if aviation would not exist? Some things would be:
Poverty wouldn't be fought against with the same degree of practicality and relative easiness by sending humanitarian aid to different parts of the world in a matter of days or hours. There would be no landing strips or runways, no parachutes for air dropping of food and medicines and no white UN aircraft taking refugees out of disaster regions.
Financial markets would move much slower because the overall speed of practical communications and commercial exchange would be far lower than today.
Governments would have far less political and military power since the concept of an air force would not be real. Tyrannies such as the Third Reich could not have been fought in the way they were, because during WWII air power proved to be the only way to debilitate the Nazi regime and the one in Japan y means of remote attacks when it would otherwise have been impossible to do by naval or terrestrial means, at least during most of the stages of that conflict.
Many families of people who migrate to distant lands would still be torn apart forever; cheap air travel is what makes it possible for relatives and friends to reunite.
All this and even more would take place if people like the Wright brothers, professor Langley and the Lilienthals wouldn't have bothered to develop aviation, an activity that was seen as a useless, dangerous and impossible quest just a few years before human flight was achieved. Thanks to their efforts the world changed so much in a century that life without flight would be almost unconceivable for most people today. Meanwhile, humanity spend its resources on more "useful" things like stupid ideologies that killed millions of people, we entertained ourselves with two world wars and an assortment of others, various financial crises and all sorts of political squabbles initiated thanks to the "better judgement" of those opposed to science and technology or the individuals and institutions that should be in charge of managing the resources of nations.
Poverty and other social issues and shortcomings will never be solved by denying the need for scientific and technological progress but on the contrary, because since we live in a world that is becoming more complex it appears contradictory to think that it would be thorough ignorance that we would solve our problems. Indeed, things are not ideal today but overall better in social terms than in the past: Many people still live in bad conditions buy at least in those countries that have embraced scientific and technological research and development as a national policy - the so-called developed countries - common people that decades or centuries ago would have lived in poverty today belong to the middle classes.
This fact alone demonstrates that research and development in science and technology is both necessary as well as inevitable. Form what has been already done in the fields of astronautics and space travel many good things have come out like telecommunications and weather satellites that have changed the lives of millions for good, despite criticism. But what becomes now more important than ever is that before we step into other planets in our system or for that matter, even exoplanets, is that we should not take our own shortcomings there.
If we cannot understand the importance of things like this, we may not be able to avoid the destruction of other worlds.