When my colleagues and I walk the streets of our cities and talk to people about privacy, a surprising number of them respond that they have no need for it. That’s not just surprising, that’s dangerous.

Damage from mass surveillance is quite a bit like damage from radioactivity. The devastating consequences are only apparent to society as a whole ten, fifteen, maybe twenty years later. Therefore, it is easy to dismiss the dangers of something you can’t see, touch, or smell as you walk in the street – but we know all too well what happens, as we have many blueprints of history and its lessons to fall back on.

Imagine for a moment that somebody was listening in to everything you said on the phone. Would you think twice about what you said? Probably. You’d probably refrain from discussing some things you wanted to keep strictly between the person you were talking to and yourself, and save those discussions for a face-to-face meeting where the other person wasn’t listening in.

Well, the good news is that you don’t have to imagine it: thanks to the revelations of Edward Snowden, we know that everything is wiretapped, at least if it happens to pass by one of the wiretapping points of the NSA/GCHQ network, which you have no way of knowing in advance. While not everything may be picked out for closer analysis, neither were the steamed-open letters in East Germany, and yet people shunned that practice.

In countries where the Data Retention Directive has been implemented, where our mobile phones are turned into governmental tracking devices and every call logged (not its spoken words, but merely that the call took place), slightly over half of the people have hesitated or refrained from making phone calls that could be used against them in the future: psychologists, drug addiction helplines, et cetera. Over half. Not in some far-fetched future scenario; this is what has already happened.

And here’s one key observation of why we need privacy: Because we have a fundamental need to keep some things to ourselves. The alternative to privacy is not being open about our problems and concerns, the alternative is not discussing our concerns at all, as we have already seen from the numbers. Out of fear that our weaknesses, our everyday habits, or just who we were born to be will one day be turned against us.

This is also why we have medical privacy – so that people with problems can get help with those problems, without fear of having their problems turned against them. It should be obvious that it is in society’s greater interest to help its citizens, and yet, a mass surveillance makes this hard or impossible.

The resulting ominous silence is also exactly what history tells us will happen, and that is why the people in the streets shrugging their shoulders are dangerous: most of them assume that since they have no need for privacy, those people also don’t mind new laws that deprive others of theirs. But that, obviously, negates other people’s ability to choose for themselves.

At the end of the day, everybody’s privacy is their own responsibility. The world as we know it has shown that you can trust no one but yourself to keep your secrets safe, and that you probably need a selection of tools and habits to do so.

A secret told, after all, is not a secret anymore. The same thing goes for a secret overheard, or a secret wiretapped.