Terrorist activity has reached the highest level ever recorded, according to the Institute for Economics and Peace. And yet, Americans are still more likely to die in a lightning strike or a bathtub than in a terrorist attack, an argument originally made by John Mueller in his 2006 book, Overblown.

Nevertheless, acts of terror are tangible—their gore, death tallies, and elevated warning levels flash across our television screens—and produce statistics at every turn, so they offer the U.S. government an implicit mandate to continue its mass surveillance programs. Programs that undermine the privacy protections constitutionally guaranteed to every American.

They work because surveillance isn’t easily quantifiable. It’s clandestine, invisibly operating beneath our fingertips, siphoning away our data and with it, our ability to vet the consequences. Admittedly, it’s hard to get excited about the slow erosion of our civil liberties.

But it’s time to level the playing field, with more investigation into the cold, hard—and chilling—effects of government surveillance.

A steadfast commitment to freedom of expression and privacy—even in the midst of threat—is what sets democracies apart from the rest of the world. However, the U.S.’s commitment is waning. Reporters sans Frontières ranks the United States 49th in terms of press freedoms, which means we have fallen out of the top quartile of countries in the world in protecting expression. Let that sink in. America, the longstanding beacon of free speech, performs worse than some partly democratic countries in the global south, like Burkina Faso and Niger. Our nation’s whistleblowers and journalists are not adequately shielded from undue prosecution and self-censorship. Nor are our citizens.

Despite this statistic, large swathes of the American public think they’re impervious to surveillance, as if opposition raises suspicions of guilt. As a researcher examining public attitudes toward surveillance, I often encounter the argument “I’ve got nothing to hide,” typically voiced in a tone of defensive indignation. But opposition to mass surveillance does not need to be grounded in defensively hiding information; it’s about the proactive protection of your online identity.

In an effort to see what average Internet users have to hide, my graduate students and I convened a short focus group to investigate if there were any types of online activities that they would like to remain private, and sure enough, they did.

Predictably, adult content, online purchases, and strange but innocuous Google searches topped the list. But we also noted some behaviors that have direct implications for democracy: discussions on online forums, browsing news sites, and social media posting. These latter three are capital-enhancing activities, meaning they have the potential to translate into political opportunities in the offline world, like acquiring the knowledge and attitudes necessary to vote, petition and protest. A suppression of these activities threatens the vibrancy of our democracy.

It was surveillance’s effect on social media posting in particular that I wanted to quantify. So I set out to conduct the first study to test how these mass surveillance programs influence average Americans’ online behavior. I exposed a group of Internet users to a “terms of agreement” statement that reminded them—as most terms of agreements do—that their subsequent actions on our site were subject to interception and surveillance. The study’s participants were then shown a Facebook interface, where they could indicate whether they wanted to comment on, share, like, or create new Facebook posts about a current political issue.

I discovered that exposure to the terms of agreement dampened individuals’ willingness to express or otherwise support their political views. These effects were found among people who felt they held political opinions different from those of most Americans, among those who thought these programs were necessary for the sake of national security, and in a recent follow-up analysis I conducted, among racial and ethnic minorities. These individuals refrained from expressing opinions that would alienate them from both their fellow citizens and from the government.

The results were, quite literally, chilling.

And surveillance chills in a way that suppresses the ideas of those on the fringes of society, while amplifying dominant, mainstream opinions. This severely undermines the Internet’s ability to serve as a neutral platform for information sharing and discussion, instead catering only those who speak the loudest.

Published online last month, this study was released right in the middle of the presidential primary campaign, when Facebook feeds were saturated with partisan endorsements and polarizing vitriol. Strangers, acquaintances, and friends approached me—almost all in person—to confide that they too had, at times, fallen victim to this type of self-censorship on social media. This study, which drew upon a sample of Internet users from across the U.S., shows its not just happening among my social network. It’s probably rampant among yours, too.

Their anxieties are not baseless. Recent reporting has shown that the U.S. federal government has poured money into private companies to monitor and mine social media content—for what, we’re not exactly sure. And data on Americans collected and achieved by the NSA may be shared with other government agencies, without a warrant, to investigate and prosecute crimes unrelated to national security and terrorism, like drug offenses.

Even for the vast majority of us who aren’t guilty of any wrongdoing, our photos, posts, check-ins, search histories, and, above all, metadata, paint detailed summaries of our online lives. We’re entitled to privacy and the ability to choose what we want to reveal about ourselves, to the government, to our employers, and to one another.

As we continue the uninterrupted march into an era of big data, this study should serve as yet another red flag, signaling the need for greater transparency, skepticism, and quantifiable research.