Do those who enjoy unprotected sex also allow restaurants to serve them contaminated food?

Nigel Wrench, one of the most famous news presenters on Radio 4, became HIV-positive in 1993 as a result of having sex on Hampstead Heath with a man who didn't want to use a condom. You would think that 1993 was a bit late to behave so foolishly and that it might have been a chastening experience. Quite the contrary. Wrench now regularly has unprotected sex - "barebacking", it's called - and, in an article in the Pink Paper and an interview in the Guardian, he wants to start a "rational debate" on the subject.

"Barebacking can be warm, exciting and involving," he states. "We need to debate it. But don't let's start by writing it off as irresponsible and stupid. That, frankly, is both absurd and dangerous."

Wrench himself protests that he only has unprotected sex with men who are also HIV- positive, which suggests some uneasiness on the subject. It might be worth pointing out that even this apparent prudence has its dubious aspect, bringing with it the risks of other sexually transmitted diseases for people already suffering from deficiencies in their immune system. And even the most cursory research suggests that there is also reason to doubt the commonsense assumption that if you are both HIV-positive, you might as well dispense with protection because you cannot be infected twice. In reality, you may be infected by a different strain and - worse still - a strain that is resistant to the treatment your partner is receiving.

But all this is really beside the point. Wrench may have done a service in discussing this issue in public - although, if I were gay, I would have very mixed feelings about these statements, which will inevitably confirm the worst homophobic prejudices about gay behaviour. It may be that we should not condemn Wrench for what he says, but is it really forbidden to criticise him for what he does? Are we now forbidden to disapprove of any sexual behaviour?

It is difficult to know where to start, but Wrench could start by being more self-critical. A black Zimbabwean or Ugandan who had been infected with HIV in the early 1990s would almost certainly now be dead or dying. Plenty of unprotected sex there, but not so much of the extremely expensive medication that Wrench and others are now receiving from the National Health Service.

In a way, behind all the deliberately shocking rhetoric about how all the responsibility should not be put on HIV-positive men to reveal their status to every sexual partner, there is a straight- forward, sensible, almost humdrum argument. If you are going to have casual sex, you cannot rely on your partners for an accurate account of their health status - concerning HIV, hepatitis, syphilis, gonorrhoea or whatever. They may not even know. Obviously, you have to take your own precautions. (The same will apply when the male contraceptive pill is invented. No sane girl will ever believe a boy who says: "It's all right. I'm on the pill.")

But why does any of this mean that we have to maintain an attitude of respect for bare- backing? This is not an issue of sexuality or prejudice, but the most basic kind of responsibility that we owe to other people. If I were infected with a contagious virus that may kill other people, then I ought to refrain from acts that put them at risk. And I don't think it is much of an argument to claim that these acts are fun, that I want to do them, that they can be "warm, exciting and involving". Many years ago, well before 1993, I wrote in this column that it was important that the stigma attached to HIV and Aids be lifted, because knowledge of who was infectious was the only weapon we had. This is still largely true today; outside the developed world, it is entirely true.

The problem is that many people still believe that homosexual sex is intrinsically wicked. Even right at the end of his life, Derek Jarman spoke movingly of how promiscuous sex had been an act of liberation for him that he still did not regret. But he hadn't known. Do we now have to prove that we are liberal by putting gay sex in some special area that is beyond any kind of judgement? Would Wrench not criticise a restaurant that knowingly served him contaminated food?

Maybe we can agree with Wrench that we shouldn't "start by writing barebacking off as irresponsible and stupid". But can I end by doing it?