Despite the way they tend to attract sf writers, there are a great many stumbling blocks in the path of anyone who dreams of building an arcology. Aside from the financial gymnastics that would be required to build and maintain a hyperstructure inhabited by tens or hundreds of thousands of people, it's a safe bet to say that the underlying technology to build a city in a box does not exist as of 2009. It's an equally safe bet, however, that solutions to those problems will be found during the course of the twenty-first century - so long as industrial civilization remains sufficiently intact to capitalize on them.
The threat of environmental degradation and collapse, as I wrote on Wednesday, may be one factor that spurs the construction of arcologies or arcology-like habitats over the next hundred years. It's hardly the only one. In a 2004 comment on the nature of Todos Santos, the arcology at the center of affairs in the Larry Niven/Jerry Pournelle novel Oath of Fealty, James Nicoll had this to say on what happened to drive people into the City in a Box:
Fear is what happened. Todos Santos existed because there were a lot of white folk and black people of a particular sort who were terrified after the riots that cleared the ground TS was built on. Once there was a huddling place for them to flee to that wouldn't cost them their jobs, they ran to it.
This probably means even without the unfortunate events of 9/11 a lot of cities couldn't build up the head of pressure needed to make people live in a society like TS (One that combines the worst aspects of a small town, a condo and a stockage deep in enemy territory) and so whatever Lord Haw Haw thinks while drinking himself blind Toronto just isn't going to be able to generate the fear to make people ignore the downsides of living in a big box. The future of TS style enclaves is in nations where sharp divides exist between groups, whether it's rich/poor, ethnic divisions or other visible differences. Think Sao Paulo, not Minneapolis.
When Oath of Fealty isn't following the brave, upstanding, forthright, free-willed, yadda-yadda "heroes" of Todos Santos as they work to suck Los Angeles dry, one of the continuing subplots involves a visiting Canadian governmental official investigating possibilities for a new arcology to be built up north. The novel ends with those possibilities being set in motion, for a northern Todos Santos that might not stand apart so sternly from its neighbors.
I think the idea's ridiculous, though considering that said Canadian official sported an honorific ("Sir") of the sort that's been verboten since 1935, at least Niven and Pournelle seem to have given Canada an even coat of paint from the unrealistic brush. While the traditional idea of the arcology has a certain attractiveness in a land with such punishing climates - the 1883 pamphlet The Dominion in 1983 described many Canadian cities as being similar to the modern concept of the arcology - I agree with James Nicoll, and I don't think that the psychological necessity is there. There's nothing to run from in Canada. Cities like Toronto, Montreal, and Vancouver don't have the same undercurrent of tension or separation that seem to pervade cities like Los Angeles. From the gilded mansions of Beverly Hills to the low-slung, barred-windowed, chipped-paint neighborhoods of Boyle Heights or South Central, there are subtle indications of a "class system" in LA - something which would be fertile ground for a fear-driven isolationist impulse, but which does not exist to nearly the same degree up north.
Los Angeles isn't unique in this respect, though. If the "fear model" of arcologies does get off the ground, I suspect that many of them will be built in Europe. European states tend to have a fractious relationship with their immigrant populations - while the idea of a Canadian ethnicity or "Canadian blood" (as opposed to First Nations, that is) is faintly ridiculous to me, countries like France, the Netherlands, Germany, Denmark, and so on have been ethnically homogeneous for most of their history - and as more and more people from Africa and the Middle East seek sanctuary in Europe, I imagine there's going to be more and more backlash from the people already there.
In France, the habitation à loyer modéré subsidized housing projects are where nearly 25% of that country's population resides, and the inhabitants seem to be disproportionately immigrants. A similar undercurrent of tension exists between the "ethnic Francais" and the immigrant community, most recently manifesting in the 2005 and 2007 civil disturbances. If arcologies could feasibly be built, I would not be surprised at all to see Arcologie Toussaint rise atop a burned-out chunk of suburban Paris, a secure refuge for "pure" French culture.
There seems to be, I think, a similar undercurrent of alienation in the United Kingdom. It goes at least as far back as Enoch Powell, who in 1968 made a speech where he described the UK as "busily engaged in heaping up its own funeral pyre" for allowing continued immigration. Today, the Daily Mail is Britain's bastion of anti-immigrant rhetoric - I didn't have to look far to find an editorial there decrying "Labour's open-door immigration policy putting Britain's burgeoning population on course for a Black-Hole-Of-Calcutta nightmare of 70 million." If All Saints, or maybe New Camelot, or Albion, ever went up in the green and pleasant land, the Mail would probably be sponsoring it.
To me, it's something I have difficulty wrapping my brain around. That may come from my upbringing, since as the most cosmopolitan city on Earth, Toronto is effectively the antithesis of an arcology - open, rambling, full of different people and different viewpoints. Arcologies may well come to dominate skylines in the years ahead, but I don't think many - if any - will rise under the maple leaf.