Lists of things worth saving from collapse and destruction can be made arbitrarily long: the wetlands, the symphony orchestra, the public library, the public transportation system, the solar sewage treatment plant... the list can go on and on. Saving something generally means preserving it in some intact, functional state, and often involves some fund-raising activities, and political lobbying to secure the much-needed funds. But in the US there is one category that never makes the list, and it is the most important one: ruins. Without much help from anyone, ruins can tell us of our history as a species. Every year millions of people flock to the Roman Forum, the Parthenon, the ruined medieval abbeys, cathedrals and castles, the pyramids at Giza, Cholula, and Chichen-Itza, and the temples at Angkor Wat.
We need not worry about some of the more spectacular sites, such as the Mall in Washington, DC. Barring some very large and unfortunate explosions, the Capitol, the White House, and other buildings surrounding the Mall will some day make a very impressive set of ruins, to rival the ruins of other imperial fora. The Manhattan skyline will make a most stunning set of ruins to be sure. Their glass envelopes long gone, the skeletons of skyscrapers will provide nesting sites for a myriad seabirds.
But some care may need to be taken if we are to preserve the ruins of all the run-down but interesting and quirky buildings that are being knocked down in many US cities, to be replaced with faceless, temporary, relentlessly utilitarian structures, whose ruins will be of no interest to posterity. The choice need not be between finding a new use for an old building and knocking it down: a better choice is to let it mellow, along with the rest of the country.
Economic collapse should make historical preservation more or less automatic, because the resources to knock down old buildings and to put up new ones will be scarce. The historical district of Charleston, South Carolina is an excellent example of just such a happy accident, which inadvertently preserved what is perhaps the most beautiful and architecturally cohesive urban landscape in North America. The combination of antebellum prosperity, fueled by slave, indigo, rice and cotton trades, followed by a lasting depression, caused Charleston to freeze in time. Although the intervening years saw much misery, looking at it now, it is hard to conceive of a happier outcome.
It is relatively cheap to take care of a ruin, and even the poorest of countries can sometimes find the resources to clear away the debris of a collapsed roof, put up some timbers to buttress a leaning wall, spread some cement atop crumbling masonry, plant some grass inside the open space enclosed by the perimeter walls, and prune back trees that might topple an otherwise sound piece of ruin. During a more prosperous spell, a bit of effort might restore a ruin to its former glory - for a time.
Even in their natural, entirely neglected state, ruins are, in fact, useful: they can provide a picturesque spot for a picnic, an instructive site for a school outing, a refuge for wildlife, a source of employment for tourist guides, and a place for archaeologists to dig around. A good ruin right in the center of a busy city is a poignant memento mori for the hurried people who rush about it. Should any of them find an empty slot in their schedules to be still for a moment, they could gain a precious bit of perspective by gazing at a ruin, thinking, sic transit gloria mundi.
These might be good points to bring up at a public meeting convened to discuss plans for knocking down yet another derelict old building.