Over the past few years, Mastodon has become the model for a friendlier kind of social network, promising to keep out the hateful or ugly content that proliferates on larger and more centralized networks. Journalists hailed it as “Twitter without Nazis” and for years, it’s generally lived up to that promise. But last week, the social network Gab migrated to Mastodon — and Mastodon’s admins have been forced to deal with the internet’s Nazi problem head-on.

The response has been messy. Many prominent Mastodon servers already moderate against racism, so Gab has faced a wave of individual blocks from individual servers. But going further has proven controversial, exposing profound questions within the community. Before the migration, one user requested that Mastodon add a hard-coded ban of Gab’s servers, so all instances would automatically cut it off. It was an extreme measure, but one they argued was warranted. “Gab has inspired mass shooters and murders,” they wrote. “You do not understand the type of threat they represent.”

Mastodon founder Eugen “Gargron” Rochko, meanwhile, believes a scorched-Earth campaign against Gab’s fork of Mastodon isn’t practical. “You have to understand it’s not actually possible to do anything platform-wide because it’s decentralized,” he tells The Verge. “I don’t have the control.”

It’s a hard problem, playing off the deepest limitations of decentralized projects like Mastodon. Mastodon arose from the idealistic open-source software movement, designed to let anybody run their own social media site. But it was never intended to support something like Gab. While Gab has no official political affiliation, it’s known as a haven for far-right or explicitly fascist users too extreme for bigger networks. Its hands-off moderation approach is antithetical to many supporters of Mastodon, whose creator has officially stated he’s “completely opposed to Gab’s project and philosophy.”

For parts of Mastodon, Gab’s move is an unfortunate byproduct of running an open platform. For others, it’s an existential threat — or an opportunity to take a moral stand.

Mastodon looks like Twitter at first glance. Users can post 500-character messages called “toots” (a name chosen by an early financial backer), repost or “boost” messages on their own timeline, and follow or privately message other users. But instead of a single site run by a company, it’s a software platform built on the open-source ActivityPub protocol. “Mastodon is essentially a way to host a social media website,” explains Rochko.

Since its launch in 2016, Mastodon users have set up thousands of these websites. (One unofficial directory lists around 2,500 as currently online.) They include generalist forums like Rochko’s own Mastodon.Social, as well as interest-based communities like Fosstodon — for open-source software enthusiasts — and Sinblr, for exiled Tumblr porn creators. Some instances are essentially experiments, like Dolphin.Town, where posts must contain only the letter “e.”

Many Mastodon instances hold users to a higher standard than bigger social networks. On Gab, meanwhile, users post a striking amount of hate content and have protested even very limited moderation. As of this writing, the Gab timeline’s first page features a warning about “International Jewry,” a string of posts with the hashtags “#eugenism” and “#ethnostate,” and a political cartoon of four lynched bodies (marked with an LGBT Pride rainbow, a Star of David, a Black Power fist, and a feminist symbol) above the caption “SOON.”

Mastodon isn’t a social networking website — it’s a way to host one yourself

Some Gab content has crossed the line into criminal activity. The UK jailed two teenage neo-Nazis in June for posting terrorist propaganda. Florida police also arrested a user last month for posting racist threats and possessing a firearm as a convicted felon. And in 2018, a man posted an anti-Semitic Gab message just before killing 11 members of a synagogue in Pittsburgh. Gab denies that it condones hatred — CEO Andrew Torba says it simply allows any speech that’s “legal in the United States” with a few exceptions. It correctly notes that Facebook and Twitter also contain hate speech and violent threats. Gab is far smaller than these sites, however, and its bad posts are particularly concentrated.

When Gab migrated to Mastodon, that content threatened to spill into the larger platform. Mastodon is organized into a “Fediverse,” which means that users on one instance can follow and interact with users from another. It helps make Mastodon feel like a single community, but by default, it could make users from one instance vulnerable to trolls from another. Fortunately, administrators can block instances, too, keeping out any posts or users from that server.

So far, that’s been the default response to Gab. Mastodon’s official site will only list instances that follow the Mastodon Server Covenant. The covenant mandates “active moderation against racism, sexism, homophobia, and transphobia” — which pretty much nixes any contact with Gab. For Rochko, it seems like the clearest way forward. “The software that powers Mastodon is released under an open-source free software license, which means anybody can use it,” he says. “And you know, that offers a great number of benefits — but some disadvantages.”

If you join a major Mastodon instance right now, chances are you won’t be connected to Gab. “All the admins that I know, that I interact with myself, have already blocked Gab,” says Rochko — including Mastodon.Social. “Essentially, they’re isolated.”

Gab may not need the Fediverse. It’s not dependent on Mastodon for hosting, payment processing, domain registration, or other basic infrastructure. While a recent Motherboard article quotes Gab saying it’s become “unstoppable” thanks to Mastodon, Mastodon really seems to solve one big problem: mobile app access.

Apple and Google both kicked Gab out of their app stores years ago. Moving to Mastodon gives users a built-in suite of apps to choose from, filling one of the social network’s biggest feature gaps. Gab had apparently returned to the Google Play Store as of July 10th, but even so, the Mastodon protocol ensures that users have lots of backup options if it’s banned again.

This has turned app access into a battlefield. Developers can lock Gab out by disabling login options to the instance or completely blocking content from its servers. And several have done just that. Mastodon lists six major mobile apps on its homepage. Four of them — the Android client Tusky and the iOS apps Toot!, Mast, and Amaroq — block Gab in some fashion.

“If hate speech is masquerading as free speech on an app I’ve built, it’s upon myself to somehow moderate that.”

Amaroq developer John Gabelmann banned Gab to avoid potential problems with the App Store. “My core objective is to keep Amaroq publicly available and to abide by all Apple policies, which keep unmoderated extremist/hateful content off the store,” he tells The Verge. “If your network is large enough and unmoderated enough to get the negative attention of Apple, Amaroq will follow Apple’s policies.”

Mast’s creator Shihab Mehboob, by contrast, blocked Gab after users requested it. He’s gotten one-star reviews from angry Gab users, but “if hate speech is masquerading as free speech on an app I’ve built, it’s upon myself to somehow moderate that and reduce it where possible,” he says. “I understand that the Fediverse is intended to be open and entirely at the user’s discretion as to what they want to see/use/partake in, but that shouldn’t cover Nazi-based ideologies. There has to be a line drawn somewhere.”

“If Google wants to ban it, they should start from their Chrome web browser.”

Other app developers maintain that this blocking doesn’t fit Mastodon’s mission. The Android-based Fedilab app’s free version initially blocked Gab because of Play Store content policy fears. But the ban has since been lifted. “I will simply not block instances with the app,” wrote Fedilab’s developer. “I clearly think that’s not my role … If you want a strong block, it’s in the hands of social network developers or your admins.”

And the developer of Subway Tooter, who goes by Tateisu, is skeptical that stores will censure apps for supporting Gab. “They can run their web app on a web browser,” Tateisu points out. “If Google wants to ban it, they should start from their Chrome web browser.”

Gab calls itself the largest Mastodon instance, boasting over a million accounts before migration. That number is almost double the user base of the previous largest listed instance, Japanese-language forum Pawoo.net, and triple the base of Mastodon.Social, the next-largest instance.

Rochko disputes the million-account statistic, since people signed up for those accounts before Gab moved to Mastodon, and we don’t know how many of them are still active. He also notes that Mastodon communities are often intentionally small; some limit registration or stop accepting new users after a certain point. While Gab has sought status as a direct peer of the “Big Tech” sites it loathes, Mastodon’s big draw is intimacy — four days after the migration, programmer Darius Kazemi published a guide specifically extolling the virtues of tiny communities.

Some Gab users have reveled in the idea that they’re invading the platform. One illustrated the move with a shot from The Shining, labeling an axe-wielding Jack Nicholson “Gab” and tagging a screaming Shelley Duvall as Mastodon. But joining Mastodon isn’t like flooding a traditional, centralized social network. If most instances block Gab, being one of the largest Mastodon nodes could be more like becoming the largest group to build a site with WordPress or start a workspace on Slack: more of a bragging right than a takeover.

Gab calls itself the biggest Mastodon node, but it’s complicated

It’s unclear how much Gab users are interacting with other parts of the Fediverse. The administrators of one prominent Mastodon instance, who asked not to be named out of fear of harassment, said they had not noticed Gab-related activity on their server. On the other hand, another admin who spoke anonymously said they had seen “an increasing number of reports from users about people picking fights and harassing users — mostly over transgender issues.”

Even without direct action, the administrator said that the basic anxiety of having Gab on the Fediverse has put people on edge. When one user misgendered another genuinely by mistake, the admin mentioned, they were also dogpiled with accusations of coming from Gab. “People are acting more paranoid, but I can’t say I blame them.”

Mastodon has certainly faced problems before Gab. Among other things, The Daily Dot reported early this year that some marginalized users felt ignored or underappreciated on the platform, including some who said they left because of problems with Rochko’s development process. But Gab’s migration seems to hit at the core of Mastodon’s mission, setting two founding principles — safety and openness — at odds with each other.

Even Gab’s de facto defenders don’t tend to argue much about its content. (The creator of Subway Tooter apologized for coming off as insensitive about “the Nazi problem.”) Instead, the battle lines seem drawn over whether to help individual users and admins avoid interacting with the instance, or whether to push Gab away from Mastodon as far as possible by any means necessary.

Mastodon is meant to be open — but it also wants to be safe

When Tusky blocked Gab, a poster on repository F-Droid suggested that the app should no longer be considered free software — saying that even if Tusky met the letter of open source law, it violated its spirit by building censorship into the code. Another user countered by asking for a “promotes bigotry” flag on Fedilab for allowing Gab logins. “This isn’t about freedom of speech. It’s about the enabling of hatred towards specific groups,” wrote the user, who says that she’s been assaulted for being a transgender woman. “I’m not asking for apps to block, only to know which apps aren’t actively fighting against intolerance of others.”

Mastodon’s conundrum is a microcosm of a much larger conflict online. The internet has given billions of people a way to amplify their voices, but the trade-offs have become tangible. Abolishing gatekeepers can allow misinformation and hate to flourish. Uncensored online forums can become co-opted by bigots and harassers, silencing their less powerful targets. And in the face of violent supremacist movements targeting real people, openness — once an uncontroversial pillar of internet culture — can seem like a hopelessly abstract principle.

Right now, Mastodon and its members are navigating between two bad options. If they completely ignore Gab, they could end up as a less welcoming community for marginalized people. But if they go to war, they risk fracturing Mastodon in the process. And either way, for the moment, Gab has arguably upstaged the work of admins and developers who have been nurturing their communities for years.

At the end of my conversation with Rochko, I ask if he has any last comments. “It’s just unfortunate that these are the circumstances that we’re talking about Mastodon again,” he tells me. “I would much prefer it was something specifically about Mastodon. Rather than, you know, Gab.”