In a September 21 post, Mark Zuckerberg shared nine steps that the site he started is taking “to protect election integrity and make sure that Facebook is a force for good in democracy” — by “actively working with the Government” and “partnering with public authorities”.

The day before that, the British prime minister, Theresa May, used the United Nations General Assembly as a forum to demand that social-media networks “ensure terrorist material [read: content that May disapproves of] is detected and removed within one to two hours”.

From the present Red Scare — “Russian election meddling” — and other nation-state attempts to limit speech they define as foreign propaganda or support for terrorism, to continuing efforts to “combat hate speech”, the cycle of demands from the Government and compliance by social-media giants are speeding up regarding what the rest of us are allowed to read, write, watch and share.

Newer social-media networks such as Minds.com and Gab.ai have been growing as the targets of these efforts abandon Facebook and Twitter. But those upstarts are themselves facing backlash of various sorts from service providers such as web hosts and domain registrars.

An increasingly important question, especially for libertarians, of both the civil and ideological variety, is: At what point does “actively working with the Government” and “partnering with public authorities” cease to be private, albeit civic-minded, market activity and become de facto government activity?

Or, to put it differently, when does it cease to be merely “you can’t talk like that in my living room” — exercise of legitimate property rights — and start becoming “you can’t talk like that, period” (censorship)?

My own answer: when Zuckerberg starts using the phrase “actively working with the Government” as if that’s a good thing, we are well into the danger zone.

Fortunately, the situation is, or at least can be, self-correcting. Companies rise and companies fall. The positions of Facebook and Twitter atop the social-media pile may seem unassailable at the moment, but there was a time when few expected a new generation of retailers to bring Montgomery Ward or Sears, Roebuck to their knees. If you’re not too young, you may remember how that turned out.

Social media already serves two masters: its users and its advertisers. One more master, the state, is one too many. If Facebook and Twitter do not stop playing with fire, let market demand for free speech burn them to the ground.

•Thomas L. Knapp is director and senior news analyst at the William Lloyd Garrison Centre for Libertarian Advocacy Journalism.