Re: They keep trying to build in deserts
The problem is that, if you put people in places where nothing grows, you will be spending a lot more resources doing things like delivering stuff to them and insulating them from the reasons that stuff won't grow. Large cities in the desert need lots of water, which obviously isn't there since it's a desert. Some ones will be lucky enough to be large cities in a desert near the coast, so desalinization is an option. However, with a country like the US, there is a lot of desert that's not near the ocean, meaning that if you put too many people there, you'll quickly drain the water that's nearby. A few large rivers, when people try to use them to provide water for millions of people and, where possible, agriculture, is going to cause serious damage to that river. You also have increased risk of fires in a place like that, and it is difficult to prevent fires from being dangerous or to keep rebuilding stuff when the fires have destroyed it.
At current levels of food production, do we really need to use all arable land for agriculture to the extent that cities are preventing us from doing so? There is more arable land in other parts of the continent which isn't farmed for various reasons, including environmental concerns and more complicated transportation routes. This is only relevant if we're building entirely new cities, since most existing cities were put on arable land because, when they were founded, they were getting more of their food supply either from the surrounding land or near the river that served as the primary method of long-range transportation, and now that there is a city there, it's not worth moving it.