Joan Bakewell: So what if people are hooked on sex?

Sex doesn't change much, I imagine. Human bodies must surely, down the ages, have embraced and coiled, licked and sucked in as many ways as its possible to imagine. They must, also, given the scarcity of room space among hunter gatherers, and the close living quarters of peasant societies, have done a good deal of watching.

Doing sex and seeing sex have nonetheless somehow become one of the great taboos of civilised societies, which construct elaborate dress and behaviour codes, kinship rules and social sanctions against too much display. But such is human fascination with the beast with two backs that given the chance, many more of us will read about and watch it than will readily sit down to a two-hour documentary about Iraq. Television thrives on such voyeurism, and from time to time its ageing worthies speak out to denounce the trend. Sir Jeremy Isaacs, founder of Channel 4, is the latest to do so.

Back in 2000 I made a series for BBC 2 called Taboo, about how the rules about sex on screen - film as well as television - are constantly changing as each new generation strives to go further than the last. The one remaining taboo at that time I declared to be the erect penis. We invited a young man into the studio to demonstrate how intrinsically harmless it was to see such a thing. Ironically, the BBC powers that be stepped in and we had to pixellate the image, which not only proved our point about taboo, but somehow converted the erect penis into a throbbing image far more suggestive than the real thing upright before me in the studio.

On The Parkinson Show on ITV, it was this very clip that the producers chose to introduce my interview, and again, it was the subject of much hilarity and rather shocked giggling in the audience. Sex is both funny, and intriguing, surprising, and titillating. No wonder it has such appeal for programme makers and viewers alike. Channel 4's current crop of shockers includes Designer Vaginas, The World's Biggest Penis and the much anticipated Wank Week. The producers of Big Brother always hope there will be plenty of sex among their contestants, and the newspapers are full of did-they, didn't-they speculation. Jeremy is right that sex is popular; there's plenty of it on Channel 4, and older folk like him - and me - are meant to be shocked.

My response is : so what? The actual exposure of the genitals on film and television has a long and tortured history. The most creepy moment when I was making Taboo was sitting with the staff of the British Board of Film Classification. They were on the lookout, frame by frame, for any display of the genital organs and any hint at actual penetration. These frames would then be required to be cut.

Such a mechanistic calculation made absolutely no difference to the eroticism of the film. It simply played to the odd resistance people have to acknowledging how they actually behave. Such rules must by now have long gone, because Michael Winterbottom's 2004 film 9 Songs featured explicit sex throughout. Indeed it was, interspersed with a sequence of pop concerts, the whole point of the movie. But even Jeremy Isaacs might not have minded.

What I believe lies behind his rage and distress is not the sex itself, but a quality that can apply to almost any programme: a certain seediness that seems to affect cheap and nasty programmes made to win ratings. Such programmes are commissioned and found acceptable by programme planners who are themselves not seedy at all.

This isn't the dirty mac brigade who once climbed over the stalls in the Windmill Theatre to get a closer look at the static nudes of the 1940s. These are well educated, well mannered people who see the creation of such rubbish as a way to boost their viewing figures. It is a deeply patronising view and, perhaps, one that allows them to revert to the smutty schoolboys they once were.

When people talk about television's dumbing down, I resist their blanket condemnation. There are many fine programmes being made and transmitted if only you can find them among the sea of feeble trash. All channels - including Channel 4 - are proud of such output. But the economic pressures are vastly different now from what they were in the balmy days when Jeremy Isaacs created Channel 4, with its deliberate remit to serve minorities and seek out rare and original ideas.

Channel 4 claims it faces a funding gap of £100m when the UK switches from analogue to digital. It is looking to the Government to help bridge that gap with public funding. In such a situation, the channel must on the one hand prove its popularity, its importance within the popular culture, and it must answer to the standards of taste and judgement required by Ofcom and the DCMS. This is an equation that can't be balanced without pandering to the mass market.

It is clear that Big Brother, and the whole concept of reality television that followed it, was a brilliant breakthrough into the kind of programmes that could be both entertaining and insightful. Many such programmes are sold on sleaze, but turn out to be something better. Designer Vaginas was in fact about women seriously seeking cosmetic surgery; The F Word is a way of sexing up a programme about cooking by a foul-mouthed chef who runs seven top London restaurants. If people are hooked on sex, where's the harm? So much better, I reckon, than having them hooked on violence

joan.bakewell@virgin.net