The space program in general is pretty easy to justify. First, the space program has more than paid for itself; it's brought us so much value — from communications satellites to GPS to Tang — that if NASA were a private company they would have earned enough money to spend a few billion dollars painting the NASA logo on the Moon. And, if you'll excuse the terrible pun, curiosity is its own reward; the day we stop being curious about the world around us, over and above what we need to find our next meal, our next safe place to sleep, and our next fuck, is the day we lose an important part of what makes us human. But a thousand other skeptics and science geeks could address the proximate value of Curiosity better than I could. Instead of extolling the virtues of Curiosity, I want to look at the project as an economist.
Honji complains that Curiosity will cost "two and half billion dollars" (which I can't help but hear in Dr. Evil's voice)*. That sounds like a lot, but for an economy the size of the United States, it's chump change. Our GDP is about $14 trillion dollars, that's $14 thousand billion dollars. Assuming all Curiosity, therefore, cost 2.6/14000, i.e. a little less than 0.02% of our national economy. In comparison, 0.02% of the 2010 median household income of $45800 is $9.7, about the cost of a movie ticket. It's also almost exactly what I earn in an hour. If Honji is concerned about the cost, I'll be happy to contribute an extra hour's pay to cover his cost, and I'll generously let him use GPS without calling him a hypocrite. Indeed, I'll contribute ten hours' pay to cover me and nine other chintzy bastards.
*According to Thom Patterson at CNN.com, the cost is $2.6 billion.
More importantly, Honji claims the money could be better spent elsewhere, such as universal healthcare and housing the homeless. In this sense, Honji is thinking about the economy exactly as the capitalist ruling class would like him to think. The truth is that, never mind the triviality of NASA's entire $17+ billion budget, not even the outright waste of substantial labor and natural resources (e.g. the Iraq war, almost two hundred military bases around the world, and all the other costs of maintaining our Imperial prestige) prevents us from having universal health care and decent housing. The reason we do not have universal health care is not that it "too expensive" in any meaningful economic sense. The reason we do not have universal health care is that we as a society have decided that poor people do not deserve health care. We have homeless people because we as a society have decided that extremely poor people, including many people with severe mental illness, do not deserve to have a place to live. We have more than 8% unemployment because we as a society have decided that millions of people do not deserve to contribute their labor to society, and it is only squeamishness that prevents us from just turning them into Soylent Green. Our social ills are not in any sense economic; they are entirely moral and political. We have the society we choose, not the society that the natural world forces on us.
We cannot be limited by money itself. Money itself is a pure abstraction, a pure social construction. Money is not itself physical; at best, money represents something physical. It represents the constraints on our economic activity: we can't do everything, so we use money in a complex system to decide what we want to do. In theory, we are limited by only three things: the amount of various kinds of physical stuff (iron, germanium, carbon, water, etc.) that has been stored by nature in the Earth and in the Solar System; the amount of physical energy available to us; and the amount of human labor available. In practice, however, none of those things actually limit us. Excluding oil, we have enough stuff stored in just the Earth to last us centuries, and there are orders of magnitude more stuff waiting for us in the Solar System. We don't need oil for energy; we have again orders of magnitude more free energy falling on the Earth every year as sunlight than all the oil, coal, and natural gas in the ground. And we have not come anywhere near to harnessing the labor available from the people who currently inhabit the Earth.
In practice, the only limitations that money represents are the limits imposed by our will and imagination. We can have globally universal health care, globally universal decent housing, globally universal food security, globally universal education, and, if we were to choose to do so, we could have them in less than a decade, the time it would take to sort out the details. We do not do so not because we cannot, but because we choose not.
Fundamentally, Honji shows the attitude of the capitalist ruling class. The capitalist ruling class would like us to believe that scraps are all there is, and the best the mass of humanity can do is fight over them. This is a lie. Like Honji, the capitalist ruling class believes that the mass of humanity does not deserve greatness; indeed we do not deserve even dignity or security, and it would be a crime against justice to provide it to us.