At Bath railway station last weekend, passengers were offered a free chicken risotto that tasted faintly of plastic. They were handed tiny cans of Coke and tiny peanuts, before being advised to buckle up in case of turbulence. Then they sat back as the train roared upwards into the sky.

That didn't happen. The commuters would have been quite alarmed if it had. But should they have been any less alarmed to find themselves, on arrival at Bath, instructed to walk through a 7ft body scanner? Because that did happen.

It wasn't widely reported. I spotted it on about page 12 of a newspaper: a little colour story. It might have squeaked in for a lighthearted couple of minutes on the TV news. Quite odd for such a huge, significant and sinister change to our national culture. I'd have put it on the front page.

Since when did we surprise the public with electronic body searches, randomly as they go about their daily lives, without any reason to suspect them of anything? Have search warrants also been abandoned while I wasn't looking? May the police now turn up on a whim and rootle around in our drawers?

We seem to have swallowed the security nightmare of airports without much fuss. Someone uttered the magic words "international terrorism" and we accepted (in traditional British manner: grumbling passivity) that we must now queue for several hours, remove shoes and belts, pick up a few verrucas from the airport floor, submit to any indignity suggested and abandon all hope of travelling with hand luggage only because shampoo and toothpaste have suddenly turned fatal: if we don't surrender them at check-in and wait four hours to pick them up at the other end, PEOPLE WILL DIE.

Fine. I never liked flying anyway. But if that's now going to happen at railway stations and on ordinary streets, delaying and degrading us without even a holiday at the end of it, should we not have a little chat first? Just to make sure this isn't a massive assault on our civil liberty?

I'm not saying anyone currently intends us to live in a totalitarian state, but Lord knows they're making it easy for somebody to slip one into place later on. I don't currently intend to get fit, but putting a tracksuit in the wardrobe certainly increases the risk that I might find myself squat-thrusting a few years from now.

A lot of guff is talked about how, if you aren't doing anything wrong, you should have no objection to random searches, body scanners and CCTV. That is missing the point entirely – the point being to preserve our beautiful principle of "innocent until proven guilty", our respect for privacy and our relatively healthy power balance between ordinary citizens (subjects) and the police/government. Fiddle with any of that at your peril.

True, people are now so terrified by the thought of hidden knives that we're reluctant to speak up when we see threatening behaviour on public transport or domestic violence in the street. A certain liberty is being lost anyway, along with courtesy. Still, would you really feel safer in Bath town centre for seeing a scanner at the railway station? When you see a bouncer outside a pub, do you think it's less likely to be a "trouble pub" than if you don't see one?

But these are well-rehearsed arguments and people rarely swap sides in the freedom v security debate. The flaw in my reasoning – the weakness I'd challenge if I were debating against myself in the Oxford Union (as I so frequently do, in my dreams) – is not: "Why should law-abiding folk have anything to fear from monitoring?" but: "Why do you accord privacy an absolute value?"

Let's assume that these are the last years of privacy, a concept that will die out by the end of the century. Why shouldn't it? We're all opting out anyway, with blogs, tweets, Facebook updates and mobile phone cameras. (If you eschew all that, don't kid yourself: the phone alone means you are traceable at all times, whether using it or not.)

This delights the government, as it sets the right social mood for crime-spotting cameras, passport checks for "identity fraud" and stop-and-search policies.

Rio Ferdinand loses his case against the Sunday Mirror, so the idea that people's sex lives are their own business is going out the window again. Amazing that he brought the case at all, really: a friend of mine who spent the summer in Malibu tells of truly A-list celebrities in arranged paparazzi encounters while on holiday. That sounds like mental illness to me. At the very least, having your picture taken is evidently as addictive as nicotine.

In 100 years' time, will discretion be a forgotten historical curio, like the crinoline? Or will it creep back in as a retro fashion for romantic occasions, like the candle? ("For a cute novelty this Valentine's Day, why not make love to your partner without broadcasting it live on the webcam?")

Will we miss it when it's gone, like Joni Mitchell's trees? Or will we forget it was ever there, like Steve Brookstein's career?

The answer is: I don't know. It's an old, old thing. Quite some time ago, humans decided that we'd eat in front of each other but not defecate. The ancient soul reached for moments of seclusion and solitude.

The truth is, I have no idea why it did that, or whether privacy is something we need to stay sane. I don't know that anything valuable would actually be lost if it disappeared completely. But I do know that I don't want to find out.

I'll carry on trying to work out why, while staring at the chilling image of innocent people passing through a full-body metal detector on a British street.

www.victoriacoren.com