In my neighborhood in Brooklyn, there is an interesting venue for offering your unwanted goods to others: the sidewalk. The way it works is that when you have something that you don’t want, say, some shelving, or an old coat, but which might be useful to someone else, you put it out on the sidewalk. Everyone “from the neighborhood” knows that such goods are available for the taking. (See about 2:57 into this video on this practice.  The humor in the skateboard scene, at around 3:13, comes because the woman has transgressed the boundaries where the practice applies: you are not allowed to climb into someone’s yard and remove goods simply because they are visible from the sidewalk. And this is an important point: such local customs come with rules, even though they may never have been formalized.)

Imagine an immigrant couple to the neighborhood, say from Kansas, where no such practice exists. They are redoing the wood floor of the living room, and need to put the furniture somewhere else while doing so. Given what New York apartments are like, there is not much spare room inside. But the sidewalk is nice and wide! And they have seen other people’s furniture out on the sidewalk for a time. They stick a couple of pieces out there, and go about working on their floor.

But when they go to retrieve those pieces, they find that they are gone. They call the police and report them stolen. If enough people unfamiliar with this practice come into the neighborhood, and have conflicts over it, at some point, some city councilman will intervene, probably by banning the practice. What was a useful local custom began to produce disputes and legal charges, and eventually was made illegal. I actually saw an “immigrant” from Massachusetts (perhaps just an immigrant for the day) threatening to call the police over our local double-parking custom, in which it is permissible to block people in during the hour-and-a-half street cleaning period when one side of the street is off limits for parking. I had to inform him that the local police were well aware of the practice, as evidenced by the dozens of unticketed, double-parked cars all around us.

A key contribution of the libertarian economist and political theorist F.A. Hayek was to stress the importance of local knowledge in making our social life workable. His followers are (quite correctly) keen to point out the ways in which formal government regulations on a national or state scale will tend to be oblivious to such knowledge, and to be destructive of its functioning. For example, James C. Scott has noted how Mao, in his efforts to increase Chinese agricultural productivity, imposed farming methods on Chinese farmers that were often devastating to delicate farming eco-systems that embodied centuries of built-up local knowledge.

Thus, it is somewhat surprising that libertarian advocates of open borders have paid so little attention to the effects of mass immigration on the local knowledge base. (As noted above, this can apply to immigration from other regions of one country as well as for foreign immigration. But while an immigrant to Brooklyn from Kansas is not likely to know about our idiosyncratic sidewalk offering or parking customs, clearly he or she will share more common cultural knowledge with Brooklynites than will an immigrant from Moldova.)

Without a myriad of informal “ways we do things around here” informing our day-to-day activities, social life would become overburdened with countless regulations concerning our quotidian interactions. For instance, we don’t today need a law telling us which meals must come with silverware, and which need not do so. If we order fried chicken and fries at Popeyes, it is fine if they don’t also give us silverware, but if we order borscht and beef tongue at the Russian Tea Room, we quite rightly expect a knife, fork and spoon to come with our meal, and at no extra charge.

There are so many situations in which a new immigrant to a nation will lack the local knowledge necessary to smoothly coordinate his or her actions with locals possessing such knowledge that it is foolish to think this reality is of no significance in considering immigration law. What hour is too late to play loud music? At what time is it OK to start your power mower in the morning? How many friends can you have over before it is expected that you inform a neighbor that you are having a party? When do you hold a door open for someone a bit behind you but soon to pass through it? How long can you relax in a restaurant after your meal? How did you signal to someone that he should move over on the highway so you can pass? How long is it OK to look at a magazine at a newsstand without buying it? Can you sample the food in a olive bar? What signs indicate that a person is welcoming your flirtation, and what signs say “bugger off”? How long is holding someone’s gaze expected, and at what point does continuing to hold it become aggressive? I could go on, but you get the point. Lest anyone think such matters are trivial, they should merely peruse the history of conflict between Korean shop owners and African-American locals in American cities.

A key lesson of economics is that all choices involve trade-offs: there is no free lunch. So it is curious that many libertarian economists, so eager to point this fact out in other situations, often seem to treat immigration as if it were immune to this principle, and argue as if unlimited immigration is simply an unalloyed bundle of benefits with no associated costs.

I am not at all “anti-immigrant.” A healthy level of immigration is a positive good for a community or a nation: it keeps it open to new ideas and new ways of doing things, and helps prevent ossification. But similarly, while a healthy level of exercise is a very good thing, exercising 100 hours a week is a terrible idea. Recognizing the erosion of local knowledge in the face of large-scale immigration does not imply that immigration is uniformly undesirable: it must be weighed against the positive goods that immigration provides to a community. But it cannot be so weighed if its existence is not even acknowledged.

Gene Callahan teaches economics at SUNY Purchase and is the author of Oakeshott on Rome and America.