I've found that objections to space exploration share a fundamental axiom with the more general objections to federal funding of scientific activities of any type. Namely, that the pursuit of knowledge for its own sake is an inherently worthless activity. If that knowledge happens to have some immediate positive impact on a problem affecting presently living people, then it may be worth pursuing if such a pursuit isn't "too expensive".
While it's trivially obvious that the value of unknown knowledge is unknowable, this doesn't often occur to such people, focused as they are on the limitations of the present instead of the possibilities of the future. Even if the pursuit of knowledge for its own sake were a completely useless activity which diverted resources away from more pressing problems, societies everywhere have accepted that their tax dollars inevitably fund certain things which are unnecessary. Clean parks, public support for the arts, city fireworks on holidays, etc. Yet people generally find these latter sinks of funding less objectionable than things like space exploration and federal support for science. Perhaps it's because the enormous scientific illiteracy afflicting the populace as a whole (which can be observed simply by reading any popular journalistic account of scientific developments) places scientific developments and scientific pursuits into some mental category of "abstract, probably useless stuff".
While it's trivially obvious that the value of unknown knowledge is unknowable, this doesn't often occur to such people, focused as they are on the limitations of the present instead of the possibilities of the future. Even if the pursuit of knowledge for its own sake were a completely useless activity which diverted resources away from more pressing problems, societies everywhere have accepted that their tax dollars inevitably fund certain things which are unnecessary. Clean parks, public support for the arts, city fireworks on holidays, etc. Yet people generally find these latter sinks of funding less objectionable than things like space exploration and federal support for science. Perhaps it's because the enormous scientific illiteracy afflicting the populace as a whole (which can be observed simply by reading any popular journalistic account of scientific developments) places scientific developments and scientific pursuits into some mental category of "abstract, probably useless stuff".