"Techies were making the syllogism, if you put new technology into an existing situation, and new behaviour happens, then that technology caused the behaviour.
"But I'm saying if the new technology creates a new behaviour, it's because it was allowing motivations that were previously locked out. These tools we now have allow for new behaviours - but they don't cause them."
Had Facebook been around when he was in his 20s, he cheerfully admits, he too would have spent his youth emailing photos of himself to everyone he knew.
But even if he's right, and the internet has merely unveiled ancient truths about human behaviour, isn't it still legitimate to feel a little bit dismayed by Facebook's revelation of almost infinite narcissism?
Shirky lets out a polite but weary sigh.
"Would the world really be better off if we were to hide from ourselves the fact that teenagers waste a lot of time trying to either flirt with each other or to crack each other up? Like, to whom was this a mystery, prior to the launch of Facebook?"
He grins in good-natured amazement.
"Look, we got erotic novels, first crack out of the box, once we had printing presses. It took a century and a half for the Royal Society to start publishing the first scientific journal in English.
"So even with the sacred printing press, the first things you get serve the basest human urges.
"But the presence of the erotic novels did not prevent us from pressing the printing presses into the service of the scientific revolution.
"And so I think every bit of time spent fretting about the fact that people have base desires which they will use this medium to satisfy is a waste of time - because that's been true of every medium ever launched."
Shirky concedes that the web's ability to connect people with a common enthusiasm, however obscure or deviant, can create a dangerously distorted impression of what is healthy or normal.
"But so the question in all of this stuff, always, always, always, is: is the net trade-off better or worse for society?
"I've never been a cyber utopian. I've always understood that this is a set of trade-offs.
"So for all the normalisation of, say, paedophilia, we also get young small-town kids growing up gay who now know they're not abnormal.
"And it seems to me that the net trade-off of lessening society's ability to project a sense of normal that no one actually lives up to is a good thing.
"I don't mean to say it will therefore be an endless fountain of raindrop-flavoured kittens from now till St Swithin's day. But rather, in the same way that we've generally decided that the printing press was a good thing - and I would contrast that with television, which in my mind is an open question - rather than just saying in the panglossian way that all new technologies are an improvement, it is an on-the-balance calculation."
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