Of course, these same people assume resource wars, breakdown of governement, and unchecked population growth until mass starvation or large-scale war kills off most people. Neither of these things are even remotely necessary, and assuming them without debate reflects the underlying assumption of fringe groups both to the right and left: That all people except them are untermenschen who need to be ruled or killed.
Even so, Peak Oil is upon us. The next major target for crude oil is $200 a barrel, within a year or two. Of course, a goodly part of this is the devaluation of the dollar, but that is cold comfort for the 300 million Americans. So will this cause people to overthrow the government and burn the cities? Or will they install thermostats and power-saving light bulbs, drive their SUV less and put solar panels on the roof? OK, probably not solar panels. Because in northern Europe, we have had double the gas prices of America for years, and very little has changed. There are less SUVs, but solar panels are still only used for isolated cabins.
In the latest issue of The Economist, worldwide gains in energy efficiency was estimated at 1.5% p.a., and in the USA 2%. That is to say that with unchanged energy use, the economy could grow by 2% in the USA and 1.5% worldwide, each year. (The difference is probably due to much of the world still industrializing, while the USA is now ever more post-industrial.) Computing and telecommunication is a part of this, and has far more potential. For instance, even though teleconferencing is now a mature and well known technology, business travel by air is still growing rather than dwindling. This is because energy is still so cheap as to be negligible. Somehow I don't see business class travelers looting the airports because their flights have become too expensive. I think there is a lot of room to change behavior within the current paradigm of democracy and market economy.
In the long run, there may come a time when making more efficient processors takes more energy at the factory than you save at the offices. At that point, I suppose we shall have to choose between looting & burning or switching to Linux.