How long can Twitter hold out as the only major tech company still giving house room to Alex Jones and his conspiracy site Infowars?
On Tech Tent this week we explore how social media firms are agonising over how to police their own platforms, as they try to balance free speech with growing pressure to shut down extremist voices.
So far, Twitter has been the outlier in this debate, insisting that Alex Jones and his Infowars site have not broken its rules, and can therefore stay.
"None of this is easy," Professor Jeff Jarvis tells us. The journalist and academic - who has been a vocal advocate for the way social media companies have opened up public debate - sympathises with the stance taken by Twitter's Chief Executive Jack Dorsey.
"Dorsey has a point that if the heinous things are not happening on his platform, it makes it harder for him to act," adds Prof Jarvis.
After we spoke, CNN published an investigation showing that Infowars had repeatedly tweeted links to videos that appeared to break Twitter's rules by - for instance - encouraging the harassment of young people who had survived the Parkland school shooting.
The tweets in question were deleted following the article's publication - Twitter says this appears to have been done by someone with control over the account.
We asked for an interview with Jack Dorsey, who spoke this week to Fox News's Sean Hannity. Twitter told us he was unavailable.
When I suggest to Prof Jarvis that the likes of Twitter, Facebook and Google are having to come to terms with the fact that they are essentially media companies, he pushes back strongly.
Twitter, he says, is Times Square not the New York Times - it's about conversation not content: "Do we really expect someone to be there policing every conversation?"
He also rejects the idea that the truth is losing on the likes of Facebook and Twitter, and accuses old media of a moral panic.
"Take off your dystopian glasses," he says pointing to the fact that movements like #blacklivesmatter, #metoo and the gun control campaign by Parkland students owe their existence to social media.
Another view is that the internet has facilitated the spread of views that were once seen as completely beyond the pale in most public forums, such as holocaust denial and white supremacy.
But there are signs today that even the most extreme free speech sites have their limits.
Social network Gab has become the destination of choice for those on the alt-right who have been banned from other sites.
This week it acted to remove some posts containing extreme anti-Semitism. The move followed pressure from Microsoft whose Azure cloud service hosts the social network.
Back in 1996, America's Digital Millennium Copyright Act gave websites some immunity from the kind of legal action old media firms face if they host defamatory or hateful content.
But they are not immune from public pressure - or from tech giants concerned about their reputations.