The eruv is one of the most brilliant devices for social engineering ever invented. It’s nothing more than a length of string, really, but when draped between telephone polls and fence posts, it defines the area in which observant Jews are allowed to carry items beyond their households on Shabbat.

That’s the technical definition. What the eruv really does is define community. Like the laws of Shabbat that prohibit driving and riding, the eruv forces observant Jews to live within close proximity to their synagogues and to each other. The results, whether in crowded cities or even in spread-out suburbia, are walkable, sustainable, sprawl-resistant villages-within-villages where neighbors look after neighbors. Centuries before architects dreamed up the “new urbanism,” there was the eruv.

And yet the eruv frightens people. From Tenafly, NJ, to London, England, the construction of an eruv can put a chill in the hearts of gentiles and non-observant Jews. My friend Jonathan Tobin, editor of the Philadelphia Jewish Exponent, writes of the latest eruv squabble in the Main Line Philadelphia suburbs of Lower Merion and Bala Cynwyd. There, according to a recent article in Philadelphia magazine, longtime residents — especially non-Orthodox Jews — say an influx of Orthodox Jews is changing the character of their neighborhoods for the worse. The newcomers’ Old World Judaism is a rebuke to the “majority’s” enlightened secularism. The strict gender roles of Orthodoxy and attitudes toward homosexuality are a direct challenge to their neighbors’ notions of diversity. Perhaps worst of all, as Tobin astutely points out, these people vote conservative.

Tobin sees this as simple — and in the case of assimilated Jews playing out their own Oedipal dramas, not-so-simple — bigotry.

“Among secular Jews who have come to view all religion as negative, the prejudice against Orthodoxy is often no less visceral than the prevailing attitudes among many Jews about evangelical Christians,” writes Tobin. “As in that case, it isn’t just that their beliefs are different. It is that many of us unfairly view them as backward and inherently illegitimate.”

Tobin calls this anti-Orthodox prejudice the “dirty little secret of Jewish life,” and he’s right. It plays out whenever an Orthodox synagogue seeks to expand or announces plans to lengthen the eruv. Homeowners begin boning up on municipal codes — speaking the language of zoning ordinances and the Establishment Clause so as not to appear bigoted or politically motivated.

At the same time, I wonder if it is possible to have an honest discussion about the impact of growing Orthodox neighborhoods in a way that is neither bigoted nor political. I’m asking this because, well, I live in such a neighborhood. Although I attend a Conservative synagogue, I moved to a neighborhood that would support our kosher, Shabbat-observant lifestyle. When we decided to stop driving on Shabbat, I pledged that my kids would never regard Shabbat as a curfew, but as a day of leisure, worship, and community enjoyed in the company of kids just like them.

And I made good on the pledge, picking a community with multiple synagogues, kosher restaurants, traffic-free streets on Saturday afternoons, and Sunday soccer leagues.

But as much as I see the pleasure in this lifestyle, I also see the costs. The land rush for walking-distance real estate is creating a homogenous enclave, where diversity is defined by the color of your kipa, not your skin. Because most of our kids go to day schools and our leisure time revolves around our synagogues, interactions between Orthodox and non-Orthodox residents become few and far between.

Day schools create another dynamic: taxpayers apathetic or even hostile to local public schools, as in Lawrence, NY, where the school board is run by an Orthodox majority whose kids don’t use the schools.

Even kashrut has its consequences. What happens to the social fabric when neighbors eat in separate restaurants and can’t eat in each other’s homes?

All of this can and does breed distrust and miscommunication on all sides and limits possibilities for civic engagement. Neighbors who don’t get to know each other think the worst of each other. Kids who grow up unmindful of other races, religions, classes, and ethnicities grow up to be adults who organize politically around only their own narrow self-interests.

Jonathan Tobin is right that anti-Orthodoxy is a “troubling and disturbing trend” and that it is “high time every segment of Jewry, from secular to Orthodox, reminded themselves that their fellow Jews aren’t the enemy.”

But as someone deep within the eruv, so to speak, I also think the Orthodox need to acknowledge the countertrend, if for no other reason than to develop the ability to compensate for the consequences. What’s needed: Emphasis on community relations. Sensitivity to non-Orthodox concerns and issues. Creative outreach to demystify the religious lifestyle (even a polite “good morning” to a non-Orthodox neighbor is a start). Coalition-building and neighborly contacts where possible.

Agudath Israel of America, the fervently Orthodox group, addressed these very issues at a convention a few years back. They need to be on the agenda of all Orthodox groups, just as tolerance for the religious lifestyle needs to be on the agenda of non-Orthodox groups.

The eruv, after all, is only a piece of string. It doesn’t have to be a wall.