There are two kinds of historic preservation - the kind archaeologists care about where you are preserving the artifacts of an earlier civilization, and the kind the city council is interested in at the local level. We'll be discussing the latter here. (You can read about my earlier thoughts on historic preservation in The Case Against Historical Districts.)
The primary motivation of historic preservation is to prevent something from being replaced by something worse. "Worse" is subjective, and depending on the context, could mean replacing a beautiful ornate building with a glass tower, replacing a simple two story brick building with a parking lot, or the modernization of an entire city district.
Cities and neighborhoods are not always in a state of continuous growth. When a city grows and the number of residents and businesses in the city increases, the number of housing units and floorspace for offices, retail, industry, and other uses must increase to accommodate the additional demand.
When the population decreases, it contracts. There are many ways the contraction can play out, but it could look something like this: property owners can’t find enough tenants, so the upper floors are abandoned. Eventually, rents fall so low that that the owner is collecting less revenue than what it costs to do basic maintenance on the building, so they want to get rid of the building. To stop losing money, the owner either abandons the building or sells it. If the building is sold, the new owner might think think that it is worth more to them as a parking lot than a vacant building not bringing in any money. If the building is abandoned, it deteriorates beyond repair and is eventually bulldozed. Regardless of how this scenario plays out, the net result is that it shrinks the supply of unneeded floor space in the city. This can either happen at the neighborhood level (everyone flees a former bustling neighborhood to the newly built suburbs) or even at the city level.
Historically, when the wealthiest people live in the middle of a city (often the place that has the concentration of wealth to sustain the best services, amenities, and convenience) and the poor live on the outskirts - often in a shanty town - a shrinking city would contract at its borders. Falling rent - due to falling demand but a stable supply of housing - would cause prices to decrease, so residents can afford a place that used to be only affordable for folks one step higher along the income-chain, and the crudely built shacks on the edge of town would be the first to be abandoned as the residents gravitated inwards.
Unfortunately, in the conventional American pattern of the late 20th century, where the wealthiest live on the outskirts in the shiny and new suburbs - and anyone who could afford to flee the inner city for the shiny and new stuff often did - the first stuff to be abandoned was the inner neighborhoods. There is very little you can do to stop the hollowing out of cities that are shrinking. The default reaction of city councils is to label the area a "Historic District" in a desperate attempt to slow down the decline. We can not always prevent a city from shrinking, but I think cities under these circumstances should focus on ways to bring the remaining people back into the center of town rather than pushing them to the edge, so that the city contracts and the remaining wealth concentrates together, instead of hollowing out.
Onward and Upward
On the other hand, even without a shrinking population, some places are no longer relevant because of changing circumstances. Railway stations are typically custom built for their purpose - they have a ticketing office, a waiting room, and platforms for boarding the train. This can make them difficult to repurpose if, say, the town loses train service.
Typically when something is demolished (and it is not abandoned or has been sitting vacant and losing money), this demolition is done in order to replace the building with something that is better. When Grand Central Terminal was built, several blocks of buildings had to be demolished to make space for it. The same thing occurred when the Rockefeller Center was built. We consider Grand Central Terminal and the Rockefeller Center national landmarks today.
It didn’t seem to bother us back then, and I suspect half the reason was that, for every row house we were knocking down at the start of the 20th century to replace with something else, several dozen row houses were popping up in a newly built neighborhoods elsewhere. Collectively, we felt we were not losing anything by knocking things down as more would be built. The story is much different today, as we’re no longer steamrolling out new quality urban places to replace the few buildings we lose from a single redevelopment.
A Taste of Modernity
Second - I believe historic preservation is largely the result of modern architecture. There is certainly some nice modern architecture, but a lot of it is junk. I could go on with my criticism of modern architecture - it looks like the same generic building regardless of if it’s in France, the United States, or China. When done at a large scale, modern architecture - with its large-scale features and blank surfaces - is just exhausting to walk past.
San Juan is a beautiful city. Cities such as San Juan, recognizing that they have something great, tend to lock down the oldest part of their city from changing under the label of historic preservation. I do not disagree that Old San Juan is great. But, what is unsettling to me is that when cities like San Juan and others around the world attempt to ‘preserve’ the city by preventing all development and change, they are basically choosing some arbitrary date - such as 1930 - at which the city was perfect and must be preserved as is forevermore, and after which all development is bad and is destroying the character of the city.
A Living, Evolving Entity
A city is a living, evolving entity. If we were in the habit of locking down cities to preserve them centuries ago, many of our cities would not have progressed past the shacks that the pioneers lived in. But, we understand that incremental progress - the replacement of the older with the newer - was good and built these places into the cities that they are now. Given the last three quarters of a century of modern architecture and city planning, it is easy to see how people can be suspicious of change - where development is now synonymous with taking the old and ornate and replacing it with the new and generic. Thus, motivating the case to want to ‘preserve’ Old San Juan.
You see, if modern architecture and city planning were rejected by the Puerto Rican people and Old San Juan was the default development pattern the island, they would have continued building in this pattern, and there would be no need to take action to historically protect it, and we would not have a limited supply of these pockets of beautiful urbanism where only the wealthy can afford to live.
I believe there is a time and a place for historic preservation. When a particular site plays a role in history or is such a recognizable landmark, and a developer wants to tear it down or abandon it, then we have a justifiable case for preserving it. But, in most cases I believe that historic preservation is a pill for treating a symptom rather than curing the cause. We have a shortage of high quality urban places not just in the United States, but globally, and I think modernity (which includes suburbanization, modern city planning, and modern architecture) plays a huge role in this shortage. Because there is a shortage, we so desperately hold on to the places that remain. But instead, I think we should focus our efforts on tackling the underlying problem. If we were building more lovable, fine-grain, human-scale places to replace those that were lost or redeveloped, there would be very little reason to focus so much effort on historic preservation.