True about money doing 'better things on Earth', but your not taking one thing into account. The new wave of tecnology coming along. We've got two kinds coming, nanotech(which will lead to cheaper, quicker, better manufacturing so people will be able to buy more), and genetic technology, which will give us the ability for an unlimited food resource. Nanotech would also most likely make medical care more available to everyone. So this technology has the ability to eliminate famine and poverty.
So we would have A LOT of extra money to spend on projects like space. Space-based technology can also help solve energy problems here on Earth(untold amounts of resources in space). It was mentioned by one person that we can't fuel it far enough. Actually there are ways to do it.
"The technique is called inertial electrostatic confinement (IEC), a technique that avoids the use of massive magnets and laser systems used in other fusion-power techniques. Instead, the IEC device uses a hollow cathode, and the natural charges of electrons and ions, to form virtual electrodes that confine ions in a spherical region at the center of the 61 cm (2 ft) diameter IEC vacuum chamber.
"The SBIR funding has allowed us to make some historic advances," Nadler told the audience. Using a pulsed megawatt power supply, the IEC achieved its highest pulsed current yet - 17 amps at 40,000 volts. The IEC has also gone from producing one neutron (released by deuterium-deuterium fusion) in every 10 cycles to more than 100 neutrons per cycle.
"I'm happy to report that everything is looking good for increased reactivity," he said. "And we haven't even stressed anything out yet."
IEC fusion would work best with a couple of unusual fusion cycles. One uses deuterium (heavy hydrogen), easily refined from water on Earth, and helium 3 (helium lacking one neutron), quite rare here but possibly abundant in lunar soil exposed to 4 billion years of solar wind. The other fires protons into boron 11."
http://science.nasa.gov/newhome/headlines/prop12apr99_1.htm 
