0. The Moon is not "seismically dead." 1. The Moon has not cooled and solidified. 2. We do not have existing technology to create massive underground Moon fac

0. The Moon is not "seismically dead." 1. The Moon has not cooled and solidified. 2. We do not have existing technology to create massive underground Moon factories. It would be unbelievably difficult, even on Earth, to drill 500 miles into basalt, let alone doing so in mostly vacuum. This is not an unsolvable problem, mind you, but probably more difficult than you are thinking and definitely more difficult than burying some prefabricated modules beneath a few meters of lunar regolith. 3. There are about 7.3 billion humans alive right now. We have no (current) need to put hundreds of billions of humans anywhere. And the Moon could not support such a population even under the absolute best colonization schemes unless we genetically engineer humans to be smaller and use fewer resources. Again, not impossible, but not possible with current technology and may not be morally correct even if it was possible. 4. Why would we need weapons systems on the Moon? We currently have treaties against militarizing outer space. You're not seriously proposing that as a defense against alien invasion are you? If extraterrestrial life exists and possesses the technology to cross interstellar space and is belligerent, something tells me they would not have any problems defeating us even if we did bury ourselves under the Moon. Again, the Moon is simply not very interesting beyond a trial run for more complex colonization schemes for a place like Mars. If we do find some reason to colonize the Moon, we could do so fairly easily - probably within 10-25 years. IMHO, the biggest problem we would face is just getting stuff there to support people. I am very sympathetic to the insurance argument, but for different reasons. An asteroid/comet collision is much more likely to trigger the need for that than any alien invasion. But even then, depending on the size of the impact object, being on the Moon may not do us much good if the impact kicks up enough debris. But what you are proposing is pretty far beyond what we are currently capable of. Not impossible but certainly not easy or likely within the next century. [0] https://en.wikipedia.org/wiki/Quake_(natural_phenomenon)#Moonquake https://en.wikipedia.org/wiki/Quake_(natural_phenomenon)#Moo... [1] https://en.wikipedia.org/wiki/Internal_structure_of_the_Moon#Core https://en.wikipedia.org/wiki/Internal_structure_of_the_Moon... [3] http://www.census.gov/popclock/ http://www.census.gov/popclock/ [4] https://en.wikipedia.org/wiki/Outer_Space_Treaty https://en.wikipedia.org/wiki/Outer_Space_Treaty