There's a poser which the Guardian's Rosanna Greenstreet sometimes includes in her weekly Q&A feature. It's this: 'What do you consider the most over-rated virtue?' Lots of interviewees are unsure how to answer this question, but it's a very good one for those who enjoy a bit of outside-the-box heretical thinking over their Saturday croissants. 'Pride' and 'Piety' are two popular, if rather dull, answers.

However, there's another p-word that would fit the bill perfectly, and - in the unlikely event that Greenstreet ever strides in our direction brandishing her questionnaire and a couple of leaky biros - we'd offer it gladly. The most over-rated virtue is this: positivity.

It's over-rated because, as a concept, it gets an unaccountably easy ride. It's assumed to be a virtue, even though it has no real meaning. Or rather, in common with that other pejorative p-word 'politically-correct', it has about eight different meanings, and yet it's invariably used as if it only has one.

Stanley Kubrick, an obsessive archivist, had a curious way of dealing with fan mail. He would scribble 'P' on the letters which were complimentary about his films and 'N' on the ones which weren't; he would then exhaustively catalogue the two sets of letters in a series of box files. We're told that, after the release of Eyes Wide Shut, it was possible to reconstruct a brand new version of Paul Hardcastle's '19'. Anyway, what's curious about Kubrick's method is that the 'N' was not used to denote derision on his part - for the letters which he considered the work of bitter, ignorant, irrelevant or crazy people, he had a third category: 'C' for 'Crank'. With the 'C' letters discarded, it seems he afforded the 'P' and 'N' letters equal respect.

Sadly, very few people - neither creatives nor consumers - seem to share Kubrick's attitude. To many, negativity is a BAD THING per se and not to be encouraged. Even if it's intelligent, heartfelt or nails a few home truths, negativity is to be mistrusted and avoided. It's bad-humoured, unsporting, ill-mannered and mean. Criticism is apparently something you should feel guilty, ashamed or furtive about, and it should be used very sparingly. Dissent is a sign of ingratitude. To them, the 'N' pile and the 'Crank' pile are the same thing.

These people are as idiotic as the terms they adopt. They talk of 'haters' and 'naysayers' and 'moaning minnies', and believe that anything which causes them to 'sit there with a big stupid grin' on their face must be unconditionally worth celebrating. But there's an awful lot of them about, and their tiresome commitment to the 'positivity = good' fallacy generally goes unchallenged. After all, who wants to spoil their party? Positivity is always good, right?

Well, no. Everything has an equal and opposite reaction, as Einstein informed us, and we like to think he was mainly talking about reviews of The IT Crowd there. Positivity and negativity are in fact two sides of the same coin - different, for sure, but one cannot exist without the other. If somebody's positive about x, they're negative about the absence of x. And vice versa. The idea of solely being positive (or indeed solely being negative) makes absolutely no sense, except to emoticon-wielding Pollyannas.

Espousing 'positivity' and denouncing 'negativity' is a completely false dichotomy. For a start, it doesn't address the way superficial positivity can actually be a destructive thing, in that it allows mediocre things to be inappropriately lionised (thus lowering the bar - the 'It's not quite as funny as Big Train, but it's still quite good' trap). And it doesn't consider the prospect that apparent 'negativity' can open people's eyes or have a beneficial impact on The Wider Picture. These morons are incapable of thinking counter-intuitively about the positive/negative distinction; they just cannot see beyond their own superficial, short-term need for a quick chuckle-fix.

Here's an analogy. Take the recent campaign by, among others, Jamie Oliver and Hugh Fearnley Whittingstall to stop supermarkets stocking battery-farmed chickens. It's a great campaign, because it seeks a positive outcome by using apparently negative tactics: they use anger and ridicule, but they do so to (a) expose what's wrong with a current situation, and (b) remove the public's blinkers. It's all about the greater good.

But this doesn't seem to happen when it comes to discussing creative endeavours. The IT Crowd is very much the sitcom equivalent of a battery-farmed chicken, but campaigning against it isn't encouraged. Those who dislike it are expected to either ignore the programme completely or bloodymindedly search out the least offensive bits. An attitude which wouldn't go down quite so well at a chicken protest: 'I've decided to stop moaning about chickens and simply eat food I enjoy instead! And anyway, the feathers are quite pretty...'

Some will argue that, since the treatment of chickens is an important issue and comedy is pretty trivial, the above comparison is ludicrous. Well, not really. You can, after all, emotively load the question another way and ask 'What's more important - art and culture, or the fate of a few stupid birds?' Also, the idea that trivia doesn't require serious analysis seems, as a notion, unique to comedy - wine, for example, is every bit as trivial, but a wine critic who simply wrote 'It tasted nice and got me pissed' wouldn't last long on Decanter magazine.

However, even allowing for the fact that comedy doesn't involve literal pain (although anyone who's seen Lab Rats may disagree on that point), it doesn't change the validity of the analogy: just because something is trivial doesn't mean passionate criticism is misjudged or inappropriate. Media twonks they may well be, but Oliver and Fearnley-Whittingstall care about proper food the way some of us care about proper comedy. They're positive about their negativity.

The other difference between chickens and comedy, as the Pollyannas will endlessly remind us, is that the former is objective and the latter is subjective. Well, dur. The trouble is, too many people use the subjectivity of comedy as an excuse to halt the debate and declare it futile. Which is very muddled thinking indeed - after all, the fact that comedy is subjective is surely all the more reason why it should be debated.

Internet message boards are full of people who really aren't interested in discussing anything. Not only that, but they appear genuinely threatened by those who are, and so seek to turn hosepipes onto particularly fiery discussions. Saying 'Well, I liked it' after several pages of intense criticism is their usual tactic - the implication that their pissy little non-comment somehow trumps umpteen pages of erudite debate simply because it's said with a smile. But if positivity is to mean anything, it shouldn't just mean 'happy' or 'optimistic' or 'saying nice things' - it should mean 'constructive'. And constructive criticism often involves saying stuff that's ugly or unpopular. The difference should not be between positive and negative criticism, but between good and bad criticism - in other words, what should matter is how thoughtful or entertaining the analysis is, irrespective of whether it's a bouquet or a brickbat.

There are far too many people who cannot see the difference between a reasoned critique and some lunatic screaming 'IT WAS SHIT', or at least they pretend they can't. So they lump them together and dismiss it all as 'negativity'. In contrast, they'll tolerate all manner of incoherent scribblings so long as they praise shows and never bury them. These people aren't interested in comedy, or in debate - they're just terrified that one day they might have to do some actual thinking for a change. All the winking emoticons in the world won't save them.

So let's banish the word 'positivity', or at least the idea of positivity as a virtue. It's not a trait to be proud of, and it only seems to be used by debate-phobics as a reactionary way of keeping everything the same forevermore. If you see a Pollyanna, file them under 'Crank'.