Though the final stages of Aids can include periods of manic activity it is also a vandal of a disease, disfiguring before it destroys. The second anxiety concerns the tractability of the subject as a whole - what is there that dance can say about Aids but the thin apercu that it is a thoroughly bad thing? The mechanics of the illness aren't entirely inimical to creative work: Susan Sontag wrote a short story which consisted of a single unbroken chain of New York gossip, name after name passing on the dread of infection - but that was steely in its avoidance of emotion, in the conversion of the disease's social vector into a formal device. Its repetitive tedium was part of the point but would be dangerous to replicate on stage. And where television drama can deliver the fine grain of a private experience, can transport knowledge across the abyss between the healthy and the ill, dance is dependent on broader insinuations.

The worry here is that the ambiguity essential to art has been driven from the work by the urgency of the matter at hand, that the ballet simply exists as an appeal to charity. The dance critic Arlene Croce famously took this view with another dance work about Aids staged in New York describing it as "victim art", art as propaganda. These objections are subtly different - the first is a worry that the resulting piece might be bad art, and you can see why anyone might tread carefully. The idea of the corps garbed as T-cells and lymphocytes easily slips in your mind towards a queasy Busby Berkeley account of blood chemistry, like some hideously tasteless medical revue Even Mel Brooks would take a deep breath and reflect. The second is a worry that the piece might not be art at all - that it has forfeited its proper title through ulterior motives or a casual enlistment in a campaign.I haven't seen Dances with Death, so I can't comment on whether it transcends any of these little local difficulties. But the objection against art as propaganda strikes me as a slightly odd one, something contrived to cover a deeper distaste. When you come to think of it, it is far more difficult to think of art that can be guaranteed to be free of immediate designs than it is to think of examples of propaganda that has survived its purposes.

And it doesn't really matter how specific or political those purposes are: Gericault's Raft of the Medusa and David's Death of Marat were calculated interventions on behalf of particular causes - causes that, technology permitting, would have employed the full contemporary paraphernalia of mailing lists and press releases. They are propaganda, if anything is, but time has peeled away their contemporary urgencies, relegated them to a footnote in the catalogues.In this respect, the argument against art with a cause could be seen as a peculiarly selfish one, a determination to protect our own aesthetic feelings at the expense of those who follow us. Perfectly sensible, viewed in one light - why should we sacrifice our present ease on the long odds of posterity? The only problem being that the absence of propaganda is no kind of guarantee that contemporary work will be more palatable - it can just as easily issue in a bland evasion of local concerns This is a different sort of calculation. Such works sand out the serial numbers and remove all identifying badges, in the hope that their provenance and date of issue will be undetectable. They are works whose timelessness is a choice of finish, an artificial patina of detachment.It's easy to be misled, then, by the fact that great works of art don't immediately appear to display local engagements. But that is just a trick of fading, whereby certain elements are more perishable than others.

It's as wrong to think that their invisibility is an essential component of art as it would be to assume that all great paintings must have crazed surfaces. There's no reason why a ballet that set out to increase the number of blood donors, say, couldn't turn out, in time, to be great art Blinded by purpose, we'd be the last to see it.. It was a question of hype control. The makers of Trainspotting, a film portrait of a group of Scottish heroin addicts, were drinking coffee at the National Film Theatre with the chief booker from a cinema chain, pondering the wording for the poster.

Andrew Macdonald groans uncomfortably at "the best British film of the decade", and opts instead for "Hollywood, your time is up". The team, whose debut was Shallow Grave, have acquired a Britpop status in the film world, and they are anxious to prevent disappointment by controlling the hyperbole surrounding the new film in glossy reviews and youth magazines. But Trainspotting, based on the cult novel by Irvine Welsh, also carries a greater weight. The film, starring Ewan McGregor, who lost two stone for the lead role, has already been accused by more conservative critics of verging perilously close to glamorising the drugs culture. Although it shows the consequences of heroin addiction from the agony of withdrawal, it also shows the ecstatic high of a "hit" in vivid detail, has a compelling black humour, and sets the world of "smack" abuse against a soundtrack of Blur, Pulp, Lou Reed and Iggy Pop.John Hodge, a qualified doctor who adapted the novel for screen, is dismissive of the criticisms. He insists it is a straightforward account of a culture, the dangers of which are well known, that neither glamorises nor denies the reasons why people take heroin."There was no censoring in terms of what people would call taste or decency. It's an honest portrayal of the highs and the consequences, neither of which are controversial," he says.The director, Danny Boyle, says Trainspotting would have been patronising and meaningless if it had avoided showing both sides of the drugs culture "It's about the force that makes you want to take drugs.