The revelations about Prism and other forms of NSA dragnet surveillance has got some people wondering what all the fuss is. When William Hague tells us that the innocent have nothing to fear from involuntary disclosure, it raises questions about exactly what harms might come about from being spied upon. Here are some reasons you should care about privacy, disclosure and surveillance.

We're bad at privacy because the consequences of privacy disclosures are separated by a lot of time and space from the disclosures themselves. It's like trying to get good at cricket by swinging the bat, closing your eyes before you see where the ball is headed, and then being told, months later, somewhere else, where the ball went. So of course we're bad at privacy: almost all our privacy disclosures do no harm, and some of them cause grotesque harm, but when this happens, it happens so far away from the disclosure that we can't learn from it.

You should care about privacy because privacy isn't secrecy. I know what you do in the toilet, but that doesn't mean you don't want to close the door when you go in the stall.

You should care about privacy because if the data says you've done something wrong, then the person reading the data will interpret everything else you do through that light. Naked Citizens, a short, free documentary, documents several horrifying cases of police being told by computers that someone might be up to something suspicious, and thereafter interpreting everything they learn about that suspect as evidence of wrongdoing. For example, when a computer programmer named David Mery entered a tube station wearing a jacket in warm weather, an algorithm monitoring the CCTV brought him to the attention of a human operator as someone suspicious. When Mery let a train go by without boarding, the operator decided it was alarming behaviour. The police arrested him, searched him, asked him to explain every scrap of paper in his flat. A doodle consisting of random scribbles was characterised as a map of the tube station. Though he was never convicted of a crime, Mery is still on file as a potential terrorist eight years later, and can't get a visa to travel abroad. Once a computer ascribes suspiciousness to someone, everything else in that person's life becomes sinister and inexplicable.

You should care about dragnet surveillance because it gives cops bigger haystacks with proportionately fewer needles. The 9/11 Commission said that America's spooks had everything they needed to predict the attacks – but it was lost amid all the noise of overcollected data. Since then, the overcollection has gone into overdrive – the haystacks are enormous, but they still have the same number of needles in them. I want my skies safe, just like you – so I want my spooks doing their job well, not simply sucking up all the data in the hopes it it will be useful some day.

You should care about surveillance because you know people who can be compromised through disclosure: people who are gay and in the closet; people with terminal illnesses; people who are related to someone infamous for some awful crime. Those people are your friends, your neighbours, maybe your kids: they deserve a life that's as free from hassle as you are with your lucky, skeleton-free closet.

You should care about surveillance because once the system for surveillance is built into the networks and the phones, bad guys (or dirty cops) can use it to attack you. In Greece, someone used the police back door on the national phone company's switches to listen in on the prime minister during the 2005 Olympic bid. Chinese hackers used Google's lawful interception back door to hack Gmail and figure out who dissidents talked to. Our communications systems are more secure if they're designed to keep everyone out – and adding a single back door to them blows their security models up. You can't be a little bit pregnant, and the computers in your pocket and on your desk and in your walls can't be a little bit insecure. Once they're designed for surveillance, anyone who can bribe or impersonate a cop can access them.

As for Hague: if the innocent have nothing to fear from disclosure, then why did his own government demand an unprecedented system of secret courts in which evidence of UK intelligence complicity in illegal kidnapping and torture can be heard? Privacy, it appears, is totally essential for the powerful and completely worthless for the rest of us.