the idea of using space resources in space makes a lot of sense. Today, it costs upwards of $10,000 per kilogram to launch something into low earth orbit (depending on the booster - some like the Proton are a lot cheaper) and quite a bit more to reach escape velocity. While I don't have accurate numbers, it wouldn't surprise me if it cost at least 2-3 times as much per kilogram to launch something to the moon than it does to put it in LEO. That's why there's so much interest in using local materials (like water on the moon) whenever possible. Now, imagine the economies that could be achieved if we could access large quantities of construction materials and life support consumables in space.

Many years ago, Buckminster Fuller coined the term "Spaceship Earth". It's an attractive concept but, IMO, too limiting. I prefer to think of "Spaceship Solar System". There are tremendous resources in our solar system that we've hardly begun to reach. Properly harnessed solar power and materials from asteroids alone could meet humanity's energy and raw materials needs for many generations to come. It's all out there. Today, the cost is prohibitive but, as we consume inexpensive resources on Earth and develop more cost effective means to access space, the price will one day be competitive.