Donald Trump’s suggestion to ask for Bill Gates’ help in “closing that Internet up” as a way to combat terrorism was widely derided, as was his contention that people who worry about the loss of freedom of speech should parts of the Internet be closed are “foolish people.”

But saner, more sober voices than Trump’s are calling for actions even more frightening than that to fight terrorism — notably, prosecuting citizens for merely viewing websites that the government considers dangerous. Welcome to the frightening contemporary politics of antiterrorism, in which the Internet has become the favored whipping boy, and the Constitution and your rights could become the biggest victims.

Leading the charge against the Internet and the Constitution in the name of fighting terrorism is Eric Posner, professor of law at the University of Chicago. Writing in Slate, he warns that because of the Internet, “Never before in our history have enemies outside the United States been able to propagate genuinely dangerous ideas on American territory in such an effective way.” His solution: “New thinking about limits on freedom of speech.”

What would those limits be? Primarily, in his view, a law that would make it illegal for people to visit websites that glorify or support ISIS, or to distribute links to those sites or any videos, images or text taken from those sites. He would also ban people from accessing “ISIS-related recruitment social media posts.”

On a first violation, a person would be sent “a warning letter from the government.” After that, though, they would face prison sentences or fines.

The law, Posner says, is aimed only at “naive people … who are initially driven by curiosity to research ISIS on the Web.” Some people would be exempt from it, including journalists and those with “a track record of legitimate public commentary on blogs and elsewhere, academic affiliations, employment in a security agency, and the like.” So no longer would the Constitution equally protect the rights of all citizens. He would like its protection to be based on your job, your blogging history or your academic standing.

His proposal, if passed, would be one of the worst assaults in history on our rights, as well as on the Internet itself. Many law professors and civil libertarians have warned about the dangers of following his suggested path. Geoffrey R. Stone, an expert on constitutional law at the University of Chicago, is just one of many. He points to the dangers of similar past laws, such as the Sedition Act of 1798, which outlawed false statements about the government. That law was used by the Federalists in power to persecute Thomas Jefferson’s supporters.

By making it illegal to visit a website that the government considers dangerous, Posner’s law would go even beyond the Sedition Act. And it could lead to a vast surveillance infrastructure tracing what we all do on the Internet. Enforcing it would require tracking the IP address of every person who visits certain sites, then matching those IP address to specific individuals, investigating them and prosecuting them.

Today, the law would only target websites related to ISIS. But laws have a way of metastasizing once they’re passed. Who will be targeted tomorrow? Over the last several decades, there has been a substantial amount of violence that could be considered domestic terrorism against doctors and organizations that support a woman’s right to abortion, including the recent mass shooting in Colorado. Using Posner’s reasoning, could the government ban anti-abortion sites and prosecute people who visit them?

You may dismiss Posner’s ideas as those of someone on the fringes of legal respectability. But he’s anything but a legal outsider. He is a professor at one of the country’s most prestigious law schools. Between 2009 and 2013, he was the fourth most-cited legal scholar in the United States.

Today, Posner admits, his proposed law would likely be declared unconstitutional by the Supreme Court. But Stone, his fellow professor at the University of Chicago, warned in The New York Times, “Five years from now, who knows? You can imagine a scenario in which things get so terrible that you start watering down the protections.”

Let’s hope he’s wrong. The Internet in its current form couldn’t survive it — and neither would the U.S. Constitution.