The American dream used to involve a house on a green lot with a white picket fence out front. But increasingly many homeowners are opting for six-foot-tall privacy fences, completely screening their residences from the street. Taken singly, such a practice would be harmless eccentricity, but as a larger trend is indicative of the increasing isolation Americans experience from each other, as well as a blight on their neighborhoods.

Brattle Street in Cambridge, Mass. runs west from Harvard Square towards Watertown. It’s known as Tory Row because before the American Revolution the few Massachusetts colonists who were Anglican gentry built their estates on it. During the Revolution they remained loyal to Britain and were largely forced to go to Canada. But some of the houses they left, as well as houses built by the later elite of Cambridge, still exist—and are sterling examples of eighteenth- and nineteenth-century architecture. Or they would be if they could be seen.

Many of the houses along both sides of the street are hidden from view by tall privacy fences or dense plantings. The exceptions are a more recent-looking building which is home to the Lincoln Institute of Land Policy and a National Historic Site—a house that George Washington used as his military headquarters and that was later the home of Henry Wadsworth Longfellow.

It’s difficult to understand why. Sometimes it would appear that such fences are built against the noise of a busy road, but this is not the case with Brattle Street or other slow and quiet lanes. One house in the area has a four-foot fence in the front, but the street-facing windows are narrow and about six feet off the ground. They are eerily reminiscent of the embrasures or arrowslits of Medieval fortifications.

Some people have chosen to fence off their homes for security purposes. Anna Daniels of the San Diego Free Press wrote in 2013 that she and her husband built a fence in the front of their property to protect against theft and keep out hostile people asking for money. But this explanation again fails to satisfy in Cambridge, where crime is low and people almost never close the gates across the driveways anyway.

According to Eric Zorn in the Chicago Tribune, front yard fences prevent neighborhood children from playing games and provide an “illusion of added security” while making “the streetscape look like a collection of mini-compounds rather than a community.”

Rather, the phenomenon seems to indicate a withdrawal from public life. A fence stops people from looking in, but it can also prevent people from looking out. One need not concern oneself with anything on the street if one cannot see it. Social ties born of proximity and place become irrelevant. There are few “third spaces” in the neighborhood of Brattle Street and even if there were more, the automobile allows the residents to avoid interaction with each other just as if there were none. A house ceases to be a castle and becomes its own self-contained universe.

Is an area of such kings of infinite space bound up in nutshells even still a neighborhood? Maybe not.

Again, all these walls might be harmless eccentricities, but they have consequences. For one thing, we are all deprived of the ability to view fine historic architecture and by replacing it with what amounts to a featureless curtain wall, the street is made boring. This discourages walking, encourages cars to speed and, as neuroscientist Colin Ellard wrote in Aeon in 2015, boredom increases stress, addiction, and disease, and decreases intellectual activity.

“The real risks of bad design might lie less in unhappy streets filled with unmotivated pedestrians, and more in the amassing of a population of urban citizens with epidemic levels of boredom,” Ellard wrote.

The uses of trees and bushes as privacy fences can also encroach on public life by actively taking away pedestrian space when property owners don’t take care of their plantings that face the street. Pedestrians should not be forced to step into the street because cedar trees or creeping vines are taking over the sidewalk.

In less wealthy neighborhoods than Brattle Street, such fencing not only prevents there being “eyes on the street,” (in Jane Jacobs’ famous phrase), but quickly attracts the signs of blight from graffiti and litter, making walking not only boring but potentially unpleasant or dangerous.

The interaction between buildings and street life are no less important in residential neighborhoods than they are in downtown and mixed-use districts. Liveliness might be a quality reserved for downtown, but that doesn’t mean all neighborhoods can’t be friendly and pleasant to walk through.