The biggest joke of all is the Pavlovian way in which victims respond to the stimulus of the microphone
Patrice Leconte's new film Ridicule depicts a world in which wit has turned septic. Arriving in Versailles to seek assistance for a scheme to drain a malarial swamp, a young nobleman called Ponceludon de Malavoy discovers that the only route to the King's ear is through the exercise of word play - one letter short of sword play but no less deadly in its effect on the loser. Those who triumph in the court's epigrammatic duels rise ever higher, those who lose face social death - indeed, one nobleman hangs himself after falling prey to a particularly cruel joke. Despite his talent, the hero ends as the butt of a joke and leaves the court after a ringing denunciation of the malignant frivolity which has thwarted his ambition: "Today you ridicule me, tomorrow a child will die."

Noel Edmonds hasn't gone quite as far as that yet. But his objections to Chris Morris's Brass Eye, a programme which duped him into denouncing a fictitious (and manifestly preposterous) drug menace, are based on similar principles. Edmonds (a famous deceiver himself, it's worth remembering) expressed his furious disbelief that anyone could make jokes about such a serious subject, and others have taken up the refrain. By ridiculing those who concern themselves with social issues, they argue, Morris is using satire to make the world worse, a place where good intentions will always be hedged with suspicion, where the benefit of the doubt will be too hazardous a prejudice to entertain. Perhaps - dreadful thought - celebrities will think twice before they allow their names to be lent to good causes.

We can return later to the question of whether this would be detrimental to the social good. But first it's necessary to concede some anxieties about the Morris method. The programmes take the form of current affairs specials (the first was about animal cruelty, the second was about drugs) and amidst the beautifully observed pastiche of journalistic cliches there are interviews with members of the Opinionate, that amorphous assembly of spouters on which the media draws for its daily simulation of intellectual debate. The biggest joke of all is the Pavlovian way in which the victims respond to the stimulus of the microphone, apparently bypassing anything that could be dignified by the name of rational thought. Asked to comment on the case of a distressed zoo elephant that has lodged its trunk inextricably up its own rectum, Carla Lane obliged without a flicker of doubt disturbing her anguished concern.

At least, without a flicker of doubt that we were permitted to see - because you would be unwise to put too much trust in Morris's sense of fair play. Peregrine Worsthorne, invited to contribute to the same spoof programme, was visibly suspicious, but his contribution was edited in such a way that any outright challenges (and whatever reassurances were made in reply) had gone missing. What you saw there was a prank extended by the courtesy of its victim - a reluctance to say aloud what he must have been thinking: "This man is an idiot or a liar." That Morris knows how to exploit such decencies is made clear from the experience of Claire Rayner, who was invited to take part "in what I had been assured was a series on ethical issues for Channel 4, to be presented by a person new to such a task". Enlisting her sympathy for an inexperienced presenter, the makers cunningly added another little weight to the ordinary human reluctance to give strangers a hard time. From her startled looks on screen, it's clear that she thinks something very odd is going on, but isn't quite sure what to say about it.

Even if you are sympathetic to Rayner, though, her defensive article has the odd effect of converting you back to Morris's cause. "Because of this series," she writes, "it seems likely that fewer and fewer honest people who speak out on TV out of conviction will agree to do so in future." Really? Are honest people of conviction so easily deterred? And what does she mean by "conviction", exactly? She damages her own argument by admitting that a fee was involved ("I bagged the cheque they sent - you bet I did, they'd had a morning out of my busy life"). I can't speak for her, naturally, but such invitations sometimes come my way too (the beast Opinion is quite undiscriminating about who feeds it), and I know that I'm a damn sight more "busy" when the person at the other end expects me to fill their air time for free. Or does she mean by "conviction" a blithe readiness to pontificate about things you know nothing about? Watching David Amess MP reading out absurd gobbledegook about a new Czech drug called Cake (strangely plausible gobbledegook, to be fair), there's no doubting his transparent honesty, but that's still no kind of alibi. (This is, almost incredibly, the second time that Mr Amess has been gulled in this way - presumably they have to club his fingers to get him to relinquish the microphone.)

Our disbelieving laughter at such moments is not just provoked by the gullibility of individuals - and it isn't just an abuse of good intentions, either. It is a revelation of just how mechanically purposeless the machinery of public enlightenment has become. In all of this, Noel Edmonds presumably thinks of himself as Ponceludon de Malavoy - a man of wit, yes, but of social conscience, too, a man who knows where to draw the line at a joke and has fallen prey to the sneering cleverness of a corrupt elite. I'm not so sure. If there's a marsh to be drained here, it is the stagnant simmer of uninformed conviction and thoughtless urgency. Whatever you think of Brass Eye, and however uneasy you feel about its cold-heartedness, Chris Morris has, rather literally, turned over the first few sods in a project of reclamationn