First: A forum like this should be expected to have a far more "pro-space" attitude than general opinion. If I (and You too, I guess), was very negative or disinterested, we would not be here?
So to the human nature argument (especially cran): I think this is simply not correct that "it is in our nature". At least not in anything but an extremely broad sense. "Science" is simply not an universal caracteristic of humanity, if you not by "science" mean just any combination of thinking and looking at the world(then you have to be consequent and call shamanism, theosophy, oracles, soothsayings etcetera for "sciences"!) I admit doubt too, if a culture which promotes tecnological advance are more favored by "human nature", than any other culture, including those dominated by opposition to innovation. A third important point: Human "expansion" may not be natural either. In fact it is hard to see how it could be "natural". It is not written in our genes that we should colonise uninhabited territories, as little as t.ex. telescope-building, violin playing or car driving is.
Certainly there has been fully developed human societies without any of it. And certainly there could also be a future without.
That is not to say that space exploration, and astronomical science is "bad", or to deny them to be worthy undertakings, at least for some time.