I suppose every person who begins voicing their opinions about space exploration in a public forum must inevitably answer the question of "Why space?" Sometimes this is more specifically phrased as, "Why spend money on space when there are so many other problems right here on Earth?"
The latter form of the question is a trap, and I recommend that most space advocates try to avoid answering it if possible. The basic premise of the question is that we are somehow actually sending money into space where it will never to be seen again. Nothing could be further from the truth. Every dollar spent on space exploration is being reinvested in our economy. As a result, jobs are created, goods and services are produced, revenue generated, and technological advancements made. I'd like to hear the social conservatives claim that, dollar for dollar, money poured into social causes contributes nearly as much back into the economy. Compared to the perverse amount of money spent on entertainment in this country, I don't think our modest investment in space exploration can be considered socially negligent.
So, I will focus on the more general form of the question, and that is "Why explore space at all?" The answers to this question will vary from one individual to another, but you will typically see one of two kinds of responses.
The first response I refer to as the party line. The party line is usually delivered as a standard reply to those who may not share an enthusiasm for space exploration but they would still like to know why it should be relevant to them. Some examples of the party line are: the human race must spread life into the galaxy or suffer the consequences (extinction, or worse... irrelevance), must explore the frontier, give humanity a fresh start, exploit the vast resources of the solar system, etc. Occasionally, the party line is presented in such a convincing manner that converts are made. Usually though, the person merely smiles and nods and goes back to living their Earth-bound existence without even bothering to look up at the sky and wonder.
The second repsonse is the personal anecdote, and these are most often shared between people who are already have a deep and abiding passion for space and space exploration. Often, this response is much more interesting than any party line because it gives some sense of what space really means to people as individuals rather than as humanity in general. Nearly all of these stories express a strong desire, by individuals, to travel in space or explore the unknown. It is that desire that motivates so many to tackle the hard problems, to risk everything, and to see their vision become a reality. That kind of commitment speaks to the truth that it is in certain humans' nature to push back the edge of knowledge, to seek out untapped resources, and to make a better life for themselves and their posterity wherever possible. (Notice that I did not generalize this statement to encompass all of humanity as one form of the party line would have.)
My personal anecdote is alot less interesting than some others that I have read. This is probably because I'm still in the process of discovering what my true motivation is. I've had a passion for astronomy and space exploration for as long as I can remember. I am incredibly curious about the universe around me, and I've spent my entire life learning about how it works. However, getting to the root of it all - to discover what drives me and what will one day push me to truly fulfill my potential - is a long introspective journey of which I am still in the midst. In the meantime, there is a life to be lived, a universe to be appreciated, and time enough for now.