What does it cost me to go on Facebook? As I haven't got round to installing an online ad blocker, the price of connecting with my friends is that I have to endure the daily humiliation of companies trying to sell me weight loss and menopause pills. (Thanks, guys.) I've never searched for either as I'm not overweight and – well – let's not overshare. But, armed with my gender and birth date, the advertisers have made the impertinent supposition that I'm fat and flushing.

This so-called targeted advertising is the reason why Facebook was able to float for more than $100bn earlier this month. We, its users, think we are sharing our information with carefully selected friends. But Facebook is then sharing our information with advertisers all over the world. Facebook is not a benign giant kindly offering us a free service to make our world a happier place. If anything, it should be paying us for the privilege of seizing our data and selling it on.For we are not Facebook's consumers – we are its product.

Or take Google. I love its Chrome browser. And my free Google Maps app has made my A to Z atlases as redundant as the yellowing phone directory under my desk. Yet yesterday we heard that the Google street view cars that collected data for the maps were also mining private emails, photographs and texts from people's unsecured networks.

We are generally fond of Facebook, Google and Twitter because they lubricate our lives. So does petrol, though. The internet companies feel more personal because they transmit the thoughts, fears, hopes and jokes that we want to share with others online. But the business of Big Data is as impersonal and powerful as that of Big Oil – worse, because it can exploit our personal lives in a potentially far more intrusive way.

How has this happened? It's partly our fault for being so reluctant to pay for anything online. We feel entitled to something for nothing and then fail to appreciate the price of free. If Facebook were to offer its services for, say, £5 a month and promise not to share any of our data, how many of us would sign up for the premium service? My guess is 10 per cent at most.

Banks have come up against the same obstacle. We are used to free current account banking in this country, a tradition that a Bank of England director, Andrew Bailey, lamented last week. And we are reluctant to lose it. HSBC offers a paid-for package which includes such perks as "free" insurance, but nine out of 10 of its customers have chosen to remain on the free-if-in-credit tariff.

Bailey claims that free banking is a "dangerous myth" which has encouraged banks to engage in mis-selling products such as payment protection insurance. Yet,like our Facebook accounts, our current accounts aren't exactly free. We are lending the banks our money for no – or nominal – interest, which they can then lend on, in multiples, at a much higher rate. The price of free, in this case, is the return that we could have earned on our money if we had invested it.

A more dangerous myth – at least for my profession – is that good journalism can be consumed for free. If you are reading this on paper, thank you. If you are reading it online without paying a penny, you are unwittingly hastening the demise of the well-informed, independent journalism that I presume you value. For the revenue generated by online ads doesn't come anywhere close to covering the costs of producing a decent newspaper.

At a Google conference last week, I heard panellists gushing about "citizen journalists" as if they were comparable to the paid-for variety. But we don't have "citizen brain surgeons" or "citizen airline pilots". Journalism is a profession, and its practitioners spend decades building their specialist knowledge, nurturing contacts and honing their expertise so that their reportage and opinions can be better-informed than those of the man in the pub. Without that knowledge, skill and determination to find out what's really going on, the people in power would behave a lot worse. And I'm not just talking about politicians.

So we all need to think a lot harder about what we value. If you value your privacy, don't overshare and tighten your Facebook privacy settings. If you value your "free" banking, don't let the bank rip you off in other ways. And if you value the news, analysis and opinion produced by expert journalists that you read every day in your newspaper, please buy it or sign up for an app. For if you don't, the price of free is that, in a decade's time, informed journalism may cease to exist.

m.sieghart@independent.co.uk / twitter.com/MASieghart