People often give a personal explanation of whether they protect the privacy of their data. Those who don’t care much about privacy might say that they have nothing to hide. Those who do worry about it might say that keeping their personal data safe protects them from being harmed by hackers or unscrupulous companies. Both positions assume that caring about and protecting one’s privacy is a personal matter. This is a common misunderstanding.

It’s easy to assume that because some data is “personal”, protecting it is a private matter. But privacy is both a personal and a collective affair, because data is rarely used on an individual basis.

Suppose, for example, you buy a DNA testing kit. For about £100, you can hand over a sample of your saliva, along with some of your rights to your genetic data. In exchange, you will receive a report about your health and ancestry that has an average false-positive rate of about 40 per cent. Testing your DNA with a private company jeopardises your own privacy, which could have implications for whether you will get insurance coverage in the future.

Less obviously, however, your DNA test also changes the privacy of your (close and distant) kin. Although genetic information makes you who you are, we share 99.9 per cent of our genetic makeup with others. The similarities and differences amongst our genes allow inferences to be made, and your DNA could be used for all sorts of purposes. You might be happy if it helps catch a dangerous criminal in a democratic country. But what if it is used to deport refugees, or to catch political dissidents in authoritarian countries? What if your grandchildren get denied opportunities in the future on account of your genetic test? And what if your relative’s DNA test turns you into a suspect?

Genetic relationships are only one of many ways in which your privacy is interwoven with that of others. Take the Cambridge Analytica scandal. Only 270,000 Facebook users consented to the firm collecting their data. The other 87 million people were the friends of those consenting users, and their data was harvested without their knowledge or consent. Some of the people who downloaded the application that collected the data allowed Cambridge Analytica to access their private messages, again without the knowledge or consent of the people at the other side of those conversations. With the data collected, the firm built psychological profiles and tried to match them to voters around the world who were unrelated to the 87 million people whose data was stolen.

Because we are intertwined in ways that make us vulnerable to each other, we are responsible for each other’s privacy. I might, for instance, be extremely careful with my phone number and physical address. But if you have me as a contact in your mobile phone and then give access to companies to that phone, my privacy will be at risk regardless of the precautions I have taken. This is why you shouldn’t store more sensitive data than necessary in your address book, post photos of others without their permission, or even expose your own privacy unnecessarily. When you expose information about yourself, you are almost always exposing information about others.

Just as violations of privacy can be caused individually or collectively, the consequences of the erosion of privacy are also both individual and collective. As an individual, you may suffer identity theft, public humiliation, extortion, or discrimination as a result of others knowing more about you than they should. As a society, a culture of exposure can damage our social fabric, threaten our national security, and even endanger democracy.

Living in a culture in which anything you do or say might be broadcasted to millions of others puts considerable pressure on people. When we trust that others will not pass on what we say, we are more likely to be sincere, bold, and original. A culture of privacy is necessary to enjoy intimate conversations with others, have frank debates within a closed setting, and establish the bonds upon which liberal societies are based. Constant surveillance and public exposure breed conformity and silence.

Privacy can also become a matter of national security. For instance, when military personnel in the United States shared their running routes with the fitness company Strava, it didn’t occur to them that they were broadcasting the locations of military bases.

The Cambridge Analytica scandal suggested that the loss of privacy could even change the political landscape. Privacy violations enabled the construction of profiles that were used to target people with propaganda that matched their psychological tendencies. The Cambridge Analytica whistleblower, Christopher Wylie, has said he believes that Leave would not have won the Brexit referendum had the data firm not interfered. If he is right, then the loss of privacy affected everyone in the UK.

Safeguarding your privacy, then, is not only an act of self-care. It is also a way of taking care of others. It’s possible to make an analogy to climate change, in that it is a problem that can only be solved through collective action. While individuals have a part to play in cultivating a privacy-friendly culture, just like we each have a part to play in fighting climate change, solutions that rely on individual control over personal data are doomed to fail.

Given the collective nature of privacy, the dark side of the data economy can only be adequately tamed through coordinated action and effective regulation. Choosing products for their respect for privacy sends the right message to others and it gives industry a chance to see privacy as a business opportunity and innovate in our favour. Demanding that institutions protect our privacy also informs and encourages politicians to legislate for privacy. Governments and companies need to know we care about our personal data, and that the burden of protecting our privacy cannot fall on individuals alone.

Personal data is valuable, not simply because it can be sold to third parties, but because it empowers whoever has it. If we give it to companies, we are empowering them to influence our behaviour. If we give it to governments, we are empowering them to control us. Fundamentally, privacy matters because it keeps the power with the people, and this is where it should be in a democracy. So, don’t sell your privacy, and don’t give it up for free either. Defending your privacy – our privacy – is a civic duty.

Carissa Véliz is a Research Fellow at the Uehrio Centre for Practical Ethics, Oxford.

This article is part of the Agora series, a collaboration between the New Statesman and Aaron James Wendland, Professor of Philosophy at the Higher School of Economics. He tweets @ajwendland.