It doesn't require central coordination, a distributed norm enforcement network causing self-censorship is fine. In this case, it's done by Twitter: all journal

It doesn't require central coordination, a distributed norm enforcement network causing self-censorship is fine. In this case, it's done by Twitter: all journalists are on Twitter, all journalists are petrified of saying something that will upset the other journalists on Twitter, and so they all self-censor to not do that. No master plan needed.