A Supreme Court ruling against Google or Twitter would narrow Section 230’s scope and add momentum to legislative efforts to revise the law. It would also make the tech companies more gun-shy. Confronted with the risk of more lawsuits, the Internet’s gatekeepers will crack down.

Most Americans would welcome that where Islamist radicalism is concerned. But the tech companies have shown they have a distinctly partisan idea of what constitutes domestic extremism. The progressive notion of “hate speech” covers much more than the advocacy of violence.

Can the tech companies be trusted to draw the right lines between actual extremism and conservative politics that Mark Zuckerberg or Bill Gates — or some millennial manager — finds distasteful?

We already know the answer.

Progressives, for their part, are just as confident they know whether Republican legislators can be trusted to distinguish between pornography and art.

Neither party trusts the business leaders or officeholders of the other to protect its freedom of speech — including the freedom of religious speech.

Yet both parties and their allies are drawn toward imposing more constraints on Americans’ speech, taking us further down the road the tech companies have already been traveling.

Where does it end?

When the World Wide Web was in its infancy, conservatives and progressives saw unlimited possibilities in it. Conservatives could circumvent the liberal-leaning mainstream media. Progressives and libertarians celebrated the Internet’s “Do anything you want” ethos.

All expected the “information superhighway” to bring government closer to the people, fulfilling the dream of what Ross Perot called an “electronic town hall.”

The early 21st century, the golden age of blogging, posed few of the problems that seem unsolvable to today’s strictly policed social networks. There was offensive and indeed extremist material online. But to find it, one had to know where to look.

Blogs answered to no digital landlord like Facebook or Twitter. Anyone could start one, though the amount of writing necessary to sustain a blog was more than most people could attempt.

In those days, the closest thing to a social network was the informal web of links between different sites. Those links were curated by individual writers and editors.

Facebook and Twitter lowered the entry barriers. Now anyone could have a presence online and access to an already-thick network of connections.

The price of convenience and universality, however, was coming under the private governance of Big Tech: its owners, its human hall monitors and its algorithms.

Tech companies got rich, but they also came to feel they had to take moral responsibility, even if they shirked legal responsibility, for what everyone read and wrote.

So here we are. The blogs have link-rotted away, nearly everyone has a social-media presence, and Big Tech is evolving into Big Brother. Government reinforcement of Big Tech’s role as the nation’s censor seems inevitable.

With great power comes great political responsibility — even if no one thinks the tech companies are worthy of this role.

As the daylight web draws tighter, stifling legitimate speech, the unregulated dark web will predictably grow stronger. Tech censorship risks breeding the very evils it’s meant to combat.

There are only two ways out. One is to restore the decentralized messiness of the early Internet, where writers and editors were responsible only to themselves and the public law, not to corporate overlords. The other is to let Congress buy Twitter, or another network, so the protections of the First Amendment apply in the virtual town square as well as in what’s left of the real one.