Among the guests at the fabled Bilderberg meeting, held this weekend just outside London, are the top brass of Google, Amazon and Microsoft. How appropriate they should be there, alongside luminaries of the US political and military establishment. For this was the week that seemed to confirm all the old bug-eyed conspiracy theories about governments and corporations colluding to enslave the rest of us.

The Guardian revealed that the US National Security Agency has cracked open our online lives, that it can rifle through your emails, listen to your calls on Skype, watching "your ideas form as you type", as a US intelligence officer put it – apparently in cahoots with the corporate titans of the web.

This disgraces all involved, but it damages the head of the US government most. Barack Obama always had much in common with the Apple and Facebook crowd. Like them, he held out the promise of modernity – a slick, cool contrast to their creaky, throwback rivals. (Obama was rarely without BlackBerry and iPod; McCain and Romney came from the age of the manual typewriter.) But, like those early internet giants, he promised more than just an open-necked, hipper style. He would be better too. Google's informal motto is Don't be Evil. Obama's was Hope.

Perhaps people lost their innocence about Google and Facebook long ago, realising that, just because their founders were kids in jeans, they were no less red-toothed than any other capitalist behemoth. But now the president's reputation will suffer the same treatment. This Prism will dim the halo that once adorned him.

For he has authorised not merely the continuation of a programme of state surveillance that he once opposed, but has actively expanded it. That officers who serve him could brag in a 41-page presentation – one, incidentally, laced with David Brent-style grandiosity, starting with the naffness of the Prism logo – of their ability to collect data "directly from the servers" of the likes of Microsoft, Apple and Yahoo, will be a lasting stain on his record. In this, he is George W Obama.

There is a mirthless chuckle to be had from a president repeatedly slammed as a "liberal" whose legacy will be marred by a series of gravely illiberal acts.

He promised but failed to close the detention camp at Guantánamo Bay, where men have been held for more than a decade without charge (though Congress shares the blame for that). He has made routine the use of drones, assassinating enemies from the sky – repeatedly taking the innocent in the process, as he's admitted. Last month it emerged that Obama's justice department had spied on a Fox News reporter, James Rosen, tracking his movements, seizing his telephone records and taking two days' worth of his personal emails, in pursuit of a state department leak. That came after Obama had made "no apologies" for seizing two months of telephone records from Associated Press. Little wonder that the high citadel of US liberalism, the editorial column of the New York Times, this week declared that "The administration has now lost all credibility", later softening the blow by adding the words, "on this issue".

It is becoming ever harder for liberals to defend Obama. One forlorn effort I heard this week was that perhaps he did not know what the NSA was up to, even though we're told Prism is now the prime generator of material for the president's daily brief. When you're reduced to saying your hero is not evil, just useless, you know you're in trouble.

As for the web companies, their role remains unclear. Initially they insisted that the access-all-areas relationship described in Prism's PowerPoint presentation is false and there was no such collaboration. Yet one industry insider tells me that "it's very hard to think the companies did not know" the NSA was collecting their data, since such an intrusion "would show up pretty damn quick". That leaves a third possibility: that the Prism pitch was exaggerated, in order to make it a more attractive sell to its potential customers among the US – and UK – intelligence fraternity.

Whatever the truth, it's unlikely to have a lasting impact on the web giants' success. That's partly because of cynicism: plenty of us assumed these big companies abused our privacy anyway. But it's also because our relationship is one of dependence. When it emerged that Starbucks, Amazon and Google had all been paying negligible tax in the UK, it was obvious Starbucks would feel the consumer heat most, simply because it's easy to walk across the street to get a cup of coffee somewhere else. Amazon is harder to avoid and Google all but impossible. So reliant are we on these companies' services, we simply shrug and move on.

And here lies the heart of the matter, the shift in our lives that has made Prism possible. Back in the John le Carré days of cold war espionage, private information was hard to get. Spies relied on papers stuffed in manila files, or operatives hanging around on street corners, forced to gain each bit of knowledge by hand. Back then, people gave up their personal details sparingly and reluctantly.

Now we are liberal with our innermost secrets, spraying them into the public ether with a generosity our forebears could not have imagined. Where we once sent love letters in a sealed envelope, or stuck photographs of our children in a family album, now such private material is despatched to servers and clouds operated by people we don't know and will never meet. Perhaps we assume that our name, address and search preferences will be viewed by some unseen pair of corporate eyes, probably not human, and don't mind that much. We guess the worst that can happen is Google bothering us with an annoying ad or Spotify recommending Taylor Swift.

But if that knowledge goes elsewhere, if governments can get it when they ask for it, or even without asking for it, then that means something else entirely. It means that the intelligence agencies can now watch the entire population, albeit by privatised means, having in effect outsourced the job of spying to the web mega-companies.

That leaves us with a choice. Either we try to stuff this genie back in the bottle and return to the privacy habits of old. Unlikely. Or we demand companies stand firm when pressed by governments to disclose our data. Not easy. Or we demand lawmakers change the rules, restraining the executive branch's limitless appetite for information on us.

It's hard to be optimistic, for technology has made the pickings available too rich, too tempting, for the spies to resist. And, strangest of all, it is us who made this possible – by becoming informants on ourselves.