I pretty much view the whole 'Freakonomics' phenomenon with contempt, especially given the authors' blase approach to climate change, with the belief that geoengineering can save the day, is boneheaded, though not the most boneheaded approach. Generally speaking, I can't stand these guys, but while changing radio stations on my way to work last Saturday, I actually stopped and listened to their radio show, because they were covering a topic which has long been a mini-obsession of mine... the American obsession with lawns.
My take on lawns is that they are only appropriate for athletic fields of various sorts- they are wasteful monocultures, costly in terms of money spent and biodiversity lost. To me, the best symbol of the idiocy of the lawn is the suburbanites' war on the dandelion, a plant which is useful in every part, in order to grow turf grass, which is only useful to ruminants. To use potable water in order to grow this useless, invasive turf grass is extremely wasteful.
Personally, I think that a combination of native wildflower and herb/vegetable gardens is the way to go... people should at least consider having a couple of milkweed plants in their yard. I would even advocate a 'million milkweed median' program for the national highway system in order to bolster the endangered monarch butterfly population.
I listened to the entire 'Freakonomics' show, and I note that their characterization of lawns as 'carbon sinks' is flawed because it doesn't take into consideration the carbon costs of lawn maintenance and the transportation infrastructure used to support the industry, and the fact that mown turf grass doesn't remove as much carbon dioxide from the atmosphere as most plants, especially trees. I still hold the 'Freakonmics' staff in contempt, but I am pleased that they at least covered this topic.