I usually hear “suburban sprawl” from environmentalists, and they make a number of good points about sustainability, habitat destruction, water usage, and so on. Las Vegas is going to be an interesting case study in water management in a few decades.

I suspect the key to high population densities is going multilevel. There’s only such much street-level crowding people can handle, but if you go with multiple levels with high ceilings, lots of light wells, and good air circulation, you could probably make it fairly pleasant.

One of the big caveats, though, is that we don’t really have a lot of experience in building structures for the long term. In a regular city, you can knock down buildings when the cost of maintenance gets too high for the value you derive from the building, and build something more efficient in its place. How do you do that to an arcology?