Recently I've been pondering the purpose of government spending on human spaceflight. My own politics typically preempt me from such thoughts as I honestly do believe that taxes should not be collected to fund non-essential services. However, I pride myself on being able to set aside my own ideology and think like others, in the hope of learning more about their motivations and possibly even understanding their actions.
With that disclaimer out of the way, what is the legitimate role of government in human spaceflight?
In general, the government should not compete with private industry. For example, if there is domestic production of cars, it is wrong for the government to set up their own car shops. Whatever goal the government is trying to achieve by doing such can almost certainly be better served through regulation or incentives. It's wrong because of the effect it would have on the industry. With the power of the treasury behind it, the government can sell cheaper or invest more in research to make a more attractive product, and while it's true that this would appear to be a public good at first, the resulting elimination in choice as the commercial providers go out of business will inevitably lead to stagnated innovation. Without the profit incentive, all providers fail to respond to consumer demands.
As such, the government should make the fullest use of existing private industry, and encourage the development of more industry that is in the public interest. For example, when launching payloads to orbit, it would be wrong for the government to build their own rocket - or contract someone else to build one for them - if there are already rockets on the market that can serve the purpose. Furthermore, the government should plan their payloads around the capacity that is available and offer incentives for industry to improve their capabilities in the future.
In order to avoid crony capitalism, the government should use competitive bidding and punish price collusion. The government should encourage providers to create products that have customers other than the government and not place unique demands on providers - or at least, such demands should be temporary. When it is in the public interest, the government should allow providers to fail and encourage the healthy functioning of the market.
Ultimately then, what is left for government to do but hand out money to private industry and ensure it is competitive and healthy? Assuming you believe the government should be spending tax dollars, is this just "stimulus" we're talking about?
I think a lot of people see a greater role for government funded human spaceflight than just stimulus. If you agree that government should be involved whenever something is in the public interest but not in the, often short sighted, commercial interest then stimulus is probably enough, but even I see a greater role for government than this.
I often hear claims that human spaceflight is about "research" or "science" that private industry is unable (or unwilling) to do because the return on investment is not immediately apparent. To me, these claims always ring hollow as so much space research is or could be done without humans. Of course, everything I've said thus far could also be applied to robotic spaceflight but it often is already. The situation with human spaceflight seems to be somewhat different.
To me, the goal of human spaceflight has always been obvious. This may surprise some people as I regularly solicit answers to "the why question" and I never seem terribly inspired by the answers I get. The purpose of human spaceflight is to open a new frontier. I have become aware that many people don't know what this means so I will put it more crudely: the purpose of human spaceflight is to find more lands to conquer so that we don't end up weeping like Alexander the Great.
Rather than being uninspiring, some people find this answer outright distasteful. I believe this is because they think of conquering people. So far as we know, the only people in space are the six expedition crew members of the ISS, and no-one is talking about conquering them. I submit that the very first lands which humans occupied, which never before had been occupied, were conquered. I don't know why we can talk about "conquering challenges" but we can't talk about conquering space. It's the same thing, breaking through our limits to increase our sphere of influence.
Space is an especially harsh environment to conquer. It is a grand challenge as JFK described it, but I disagree that this is a reason to do it. To me, that was just a cold war way to say stimulus. The public good created by human spaceflight is the opening of a new frontier. It is a gift of opportunity that we give to the next generation.
Final thought: there are other organizations that reject the commercial interest to act in the public interest. And then we have people like Elon Musk, Bob Bigelow, Jeff Bezos and others, who act both in the commercial interest and in the greater public interest. The frontier doesn't have to be opened by a government space program but, if you've got one, at least give it the right goal.