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Neighbor turning against neighbor. Name calling. Pro-development versus slow-growth, and NIMBY versus YIMBY.

Welcome to the new hotbed of the Bay Area’s raging housing debate: locally grown social networking site Nextdoor.

From Cupertino, where controversial plans are under way to turn Vallco Mall into a massive housing, office and shopping complex; to San Jose, where a proposed Google campus could bring more than 25,000 new jobs as the region struggles with a housing shortage; to Oakland, where homeless encampments sprawl against a backdrop of new high-rise apartments, residents are arguing passionately on Nextdoor about the future of their communities and the region as a whole. The intense debates that start on the social media platform are making their way to City Hall, fueling real-life protests, petitions and ballot referendums, and even influencing local elections.

“It shapes people’s opinion,” Foster City Mayor Sam Hindi said. “It creates a lot of pressure and influence on policy makers.”

Nextdoor has expanded the Bay Area housing debate, opening the conversation to residents who don’t have the time or inclination to attend council meetings, and allowing community organizing with the click of a mouse. Neighbors trade their visions for pending developments and debate high-level solutions to the Bay Area’s housing crisis, often alongside their mayors or city council members. Others organize groups for political action. But sometimes opinionated residents clash, leading to angry online confrontations.

“Unfortunately Nextdoor has not worked out to be…a very satisfactory tool either for people who are pro-housing or people who want to set up a breather from housing,” said Bob Cushman, a leader of slow-growth group Foster City Residents for Responsible Development, who was active on Nextdoor until he was kicked off several months ago over accusations he was using the site to campaign. “It’s not monitored very well. It’s turned into a very toxic kind of site.”

San Francisco-based Nextdoor launched in 2011, promising that “when neighbors start talking, good things happen.” The platform groups users into neighborhoods, and members post about everything from lost pets to baby sitters to garage sales to break-ins on the website and mobile app. Users must prove their home address in order to join a neighborhood — of which there are 210,000, spanning eight countries — and they can’t see posts outside their own geographic area. The site declines to say how many members it has.

Like other social media sites, Nextdoor struggles to walk the line between allowing users to post freely and policing for content that violates the platform’s rules. The site prohibits attacking or insulting fellow neighbors, public shaming, political campaigning, and other behaviors, and users can flag offensive posts for possible removal. Nextdoor also relies on moderators — members who are appointed or volunteer as “neighborhood leads” — to police the platform. When a user flags a post, the leads vote on whether to remove it, or in egregious violations, recommend that the author be suspended or banned.

The housing debate is exactly the type of conversation Nextdoor wants on its platform, because it’s the epitome of a hyper-local issue, said company spokesman Steve Wymer. But it’s also an intensely emotionally and politically charged one. As a result, Nextdoor faces a constant challenge in trying to keep the discussion civil. The company is working with the nonprofit American Leadership Forum on a series of videos teaching skills for civil discourse, and intends to make those videos available to Nextdoor users.

It’s not the first time Nextdoor has had to solve behavioral problems on its platform. News outlets in 2015 and 2016 reported members used the site to racially profile their neighbors, and in response, Nextdoor began prompting people who reported suspicious activity to add more information than just the suspect’s race. But promoting civil housing discussion is trickier — there’s no algorithm for that.

“To be very blunt with you, we don’t have the solution,” Wymer said. “We want to help build community. That’s our purpose.”

Libby Lee-Egan, a 33-year-old graphic designer from Berkeley, got involved in housing politics because of Nextdoor. She saw a post about a proposed 170-unit, mixed-income housing development on San Pablo Avenue and was excited about the project, but noticed many of her neighbors commenting on the post were not. So to raise support for the development, she and her husband started messaging like-minded neighbors on Nextdoor, created an email list to share updates on the project, and wrote letters to city officials. Lee-Egan channeled that momentum into co-founding the pro-housing organization East Bay For Everyone.

Then, she says, things turned ugly. Lee-Egan says members of her Nextdoor neighborhood began attacking her and her organization, calling East Bay for Everyone a “developer front.” Someone called her a “moron,” and then accused her of being the “free speech police” when she reported it to Nextdoor.

Eventually, Lee-Egan deleted the Nextdoor app from her phone.

“It was kind of scary,” she said, “to know that people who live near me and know where I live are angry at me.” Her husband had their address on his Nextdoor profile.

Still, the San Pablo Avenue development is under construction now, and Lee-Egan feels a sense of pride every time she walks by.

In Foster City, a battle in recent months between pro-development and slow-growth residents — both with representatives serving as neighborhood leads — has led to insults, deleted posts and the banning of multiple members. Debate grew particularly hot around the proposed Pilgrim Triton project, which got the green light last fall for almost 100 new homes.

Each side accused the other of using its neighborhood leads to delete posts they didn’t agree with. Evan Adams, a 39-year-old distributor of floor coverings, and a frequent pro-housing poster, logged on one day in October to find someone had posted a picture of him on Nextdoor, taken earlier that day without his knowledge, talking to Councilman Herb Perez at a Starbucks. The poster accused Adams of making pro-housing comments at the councilman’s behest.

Many conversations, debates and fights that start on Nextdoor are having real-world impact. They’re galvanizing people to show up at City Hall, and even appear to be influencing local elections.

In Cupertino, Liang Chao, who has been a vocal critical of plans to redevelop Vallco Mall, won a city council seat in November after frequently weighing in on Nextdoor housing debates.

“A lot of people actually got to know me through my postings,” she said. But, she added, conversations on Nextdoor have become so divisive that she no longer finds the platform particularly useful.

Other politicians have found the vicious opposition they face on Nextdoor jarring. Foster City Mayor Hindi says he has friends in politics up and down the Peninsula who are wary of the site.

“You just mention Nextdoor,” he said, “and you see their face change.”