[QUOTE=Cervaise]
So apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what has the space program ever done for us?
[/QUOTE]
Brought peace? I want some of that Titan Pinot Noir, BTW. 
Unmanned exploitation of orbital space has given us a vast wealth of capability for telecommunications, climate observation, surveillence, et cetera. Unmanned exploration of the Solar System, and satellite astronomy offers a massive bounty of abstract science information. Abstract information doesn’t have an immediate payoff, of course, but eventually it often becomes very useful and even vital. Someday the capability for interplanetary flight may permit us to avoid a catastrophic event like a meteor strike. There are also massive amounts of raw materials in space–even very close to the Earth–which dwarf anything we could mine from the Earth’s crust. It’s not anywhere close to economical to exploit them now, but given advances in propulsion these may prove to be very valuable.
Manned spaceflight, on the other hand, has been a bust financially, and the scientific bounty (aside from giving us a better understanding of biological hazards in manned spaceflight) is questionable at best. The reason to keep doing it is so that we can. We’re not going to Mars in a chemical-reaction-propelled Orion capsule (despite what Bush or any talking head at NASA may say) but it is, albeit slowly and in a staggering manner, developing the necessary technology to achieve manned interplanetary flight when breakthroughs in propulsion, materials science, radiation shielding, environmental systems, et cetera are made. Whether it is worth it to do so now is a topic for debate–certainly the manner in which the United States has done so is ill-accomplished and mostly pointless–but I think it is overall a worthwhile endeavor.
However, the notion that we’re going to bodily lift the population of the Earth into space is absurd. Even with heavy lift technology like ORION nuclear pulse rockets or something similar, it’s not not conceivable, nor is there any particular need to do so. Population growth levels in the industrial world have slowed or been stopped for a couple of decades and the trend seems likely as other nations industrialize. We may eventually have a substantial human population in space, whether in orbital colonies or burrows on Mars or the Jovian moons, but these will largely be indigenous populations, the children and grandchildren of a small pool of explorers and developers, not émigrés from ecological catastrophe. If things are that bad on Earth, we won’t have the resources to build the footing to develop extra-planetary colonies.
Spinnoffs are mostly a red herring; many are not specifically spinnoffs of space exploration but rather preexisting technologies used therefore, and even those that do come from the space program could either have (and probably would have) been developed seperately or are not of critical significance to modern life. There are tangible benefits to space exploration (and almost unimaginably more to come) but citing spinnoffs is largely handwaving.
So, to the o.p., don’t focus on the Space Shuttle, about which even all but the most ardent admirers will admit to having performed diffidently at even its relatively mediocre goals. The STS was politics in action, undermining the potential of the vastly more effective and more expansive Apollo Program (particularly the proposals for Apollo Extensions and Apollo Plus), and promising operational costs and activity it couldn’t possibly have met. The future of space exploration is cheap materials (particularly precious noble metals like tantalum, iridium, and osmium that are so hard to find on Earth), non-polluting manufacturing, and averting hazards to Earth. These are worthwhile goals, non?
Stranger