I think a more apt metaphor would be, If a bunch of radicals meet at a bar, repeatedly and and loudly state their intention to murder someone, loud enough for all the employees to know, and they also get into bar fights with the people they talk about murdering...would the bar owner & employees be responsible for not intervening? For not reporting them to the police and banning them from the establishment?
But if they rented private karaoke rooms and you can't hear or see what they're talking about, just that they rent a room regularly, then you wouldn't be eh?
GP’s argument is hinged on the premise that websites can “hear” everything posted. Just because a human doesn’t see it doesn’t mean the system didn’t. They already scan all posts for their targeted ad system.
Whether that’s a valid argument or not is up to you.
The answer is yes. Yes, they would be liable.