Unless sex trafficking is something you have a specific interest in, you might not be familiar with a bill that was has been making its way through Congress, known as the Stop Enabling Sex Trafficking Act, or SESTA. The bill has already been approved by the House, and on Wednesday was overwhelmingly approved by the Senate, which means it is on its way to President Trump for approval, and if he signs it—which seems likely—SESTA will become law.

Why should you care? Because in the process of trying to combat sex trafficking, Congress could wind up endangering free speech. As CJR described in a piece on the law last year, when it was still going through the House, SESTA effectively weakens one of the key pillars of online speech: Namely, Section 230 of the Communications Decency Act of 1996. That’s the clause that gives platforms like Facebook and Google “safe harbor” for the user-generated content that appears on their platforms.

While everyone was focused on Facebook, Congress just amended the bedrock law that undergirds the internet https://t.co/nXe0fBETno via @nitashatiku — Scott Thurm (@ScottThurm) March 22, 2018

In a nutshell, Section 230 is the reason that Facebook, Google, and Twitter can distribute your tweets or status updates or video clips without being held legally liable for everything contained in them. SESTA effectively removes that protection or safe harbor in the case of anything involving sex trafficking—which wouldn’t be a problem, except for the fact that by removing that protection, free-speech advocates say it weakens the entire edifice that is Section 230.

This isn’t happening in isolation. Section 230’s safe-harbor provisions are already under fire from Congress because of the belief that they insulate platforms like Facebook or YouTube from responsibility for other kinds of speech the government doesn’t like, including Russian troll campaigns, “fake news,” sexual harassment, neo-Nazi sentiments, and anything that falls into the large and growing bucket labeled “terrorism.”

And there's more coming. When I asked @MarkWarner yesterday what regulation Facebook should face, he specifically mentioned further changes to Sec. 230 — the law that defines @facebook as a platform instead of as a publisher https://t.co/E3FPNJRbsE Sign up for CJR 's daily email — Kasie Hunt (@kasie) March 22, 2018

The risk is that if Section 230’s protections for speech are weakened—as similar protections are being weakened in Europe in an attempt to stamp out fake news and hate speech—it will give everyone from trolls to governments license to go after all kinds of speech they dislike or disagree with, because online publishers could become liable for that content. And while Facebook and Google might have the resources to deal with that, lots of small publishers and services don’t.

As Senator Ron Wyden, one of the authors of Section 230, put it during debate over the bill on Wednesday: “In the absence of Section 230, the internet as we know it would shrivel. Only the platforms run by those with deep pockets, and an even deeper bench of lawyers, would be able to make it.” In other words, the bill’s relaxation of that safe harbor for speech could entrench the dominance that Facebook, Google, and other massive platforms already have.

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Mathew Ingram is CJR’s chief digital writer. Previously, he was a senior writer with Fortune magazine. He has written about the intersection between media and technology since the earliest days of the commercial internet. His writing has been published in the Washington Post and the Financial Times as well as by Reuters and Bloomberg.