This week, listening to the Guardian science podcast, I had a treat. Caspar Melville, editor of New Humanist magazine, leader of something called the Rationalist Association, had been to see two films at the Cambridge film festival. One was a dreary creationist movie that famously misrepresented the biologists interviewed for it. This was obvious bad science, he explained. But the other was different: House of Numbers, a new film about Aids, really had something in it.

I have now seen this film. It presents itself as a naive journey by one young film-maker to discover the science behind HIV. In reality, it's a dreary and pernicious piece of Aids denialist propaganda.

All the usual ideas are there. It's antiretroviral drugs themselves that are the cause of symptoms called Aids. Or it's poverty. Or it's drug use. HIV doesn't cause Aids. Diagnostic tools don't work, Aids is simply a spurious basket diagnosis invented to sell antiretroviral medication for a wide range of unrelated problems – and the drugs don't work either.

It would take two months of columns to address all the bogus claims of this film, and that blizzard, perhaps, is the point of making it, with all the classic rhetorical devices that have been honed by Aids denialists and creationists over decades. It engages, for example, in repeated overstatement of marginal internal disagreements about the details of HIV research, to the extent that 18 doctors and scientists interviewed for the film have issued a statement saying that the director was "deceptive" in his interactions with them, that it perpetuates pseudoscience and myths, and that they were selectively quoted to make it seem as if they are in disagreement and disarray, when in fact they agree on all the important facts.

At one point there is an extended sequence explaining that you can't take a picture of the HIV virus: or maybe you can, but if you can, different scientists disagree on how, and whether their method is best.

This is an infantile world view where stuff only exists when you can easily take a photograph of it, and where the internet, compound interest and magnetism don't exist either.

There is a memorable skit on diagnostic tests, where the film-maker manages to find one woman working in a marquee in a shopping centre in Africa giving HIV tests, who accidentally misinforms him about why she is asking for information on his health risk behaviours.

In the film, this becomes a dramatic expose: the HIV diagnosis is a tautology, they suggest, a basket diagnosis for sick people of any kind who engage in risk behaviours, the blood test is unreliable, a piece of theatre, and the diagnosis is only made because the tester has asked if you are gay or inject drugs.

But people working on the frontline of HIV testing are often told to ask about risk behaviours during a test, because testing is also a great opportunity for education about prevention. Furthermore, as an interesting statistical aside, knowledge about your pre-test likelihood of having a condition also helps the tester to correctly interpret any diagnostic test.

In any case, HIV tests are so reliable that in 2007 an HIV-negative woman won $2.5m in damages after she was treated for Aids without a proper diagnosis, because there was no excuse for the mistake that her doctor made.

But am I protesting too much? As you read these words, is doubt creeping in? So tests aren't so good? So there is controversy? It's all so complicated. So many details. Maybe there's no smoke without fire. And so, maybe, I should ignore this film: but it's so profoundly misleading that you can't stop yourself.

There is an interview with Christine Maggiore, who talks about her difficult decision to go against medical advice by declining to take Aids medication, and how much better she felt as a result.

What the film doesn't tell you, as you shout at the screen, is that Christine Maggiore's daughter Eliza Jane died of Aids and PCP pneumonia three years ago, at the age of three, and, as I reported nine months ago, Christine Maggiore herself died two days after Christmas 2008 of pneumonia, aged 52 (the film finally acknowledges her death in the last 2 seconds of the film, at the end of the lengthy credits, in small letters).

We see Neville Hodgkinson, the Sunday Times health correspondent who drove their denialist reporting in the 1990s. There is Peter Duesberg, who you will remember from a recent column, when academic publishers Elsevier forcibly withdrew an article by him in one of their journals. I could go on.

Do you give idiots a wider audience when you respond to them? Are they marginal and irrelevant? I'd like to believe that they are. But the duping of Caspar Melville (who has since recanted from his uncritical response to the film, albeit only on his blog), and the attention-seeking smugness of Cambridge film festival in putting on such a moronic film, both suggest otherwise. I will never know the right way to deal with any of these people, and I will always welcome advice.