Most people are not much bothered about science, and it’s easy to fall into the lazy view that “science says X” so it must be true. Forteans (and scientists) have a more subtle view, appreciating that science is a constantly evolving process, and that the accepted truths may change over time. Every so often, a Copernicus or a Darwin shows up and turns our conceptual universe upside-down. But in their wake they leave a third group who are becoming ever more prominent: deniers. Whether it’s climate change, HIV/AIDS or evolution, the deniers can have a major impact.
Freud introduced the idea of denial as a psychological defence mechanism.  Faced with a truth that is too overwhelming, the mind rejects it, regardless of the facts. Faced with sudden dramatic news, be it the death of a friend or a million-pound lottery win, it’s quite common to hear the words “I just can’t believe it”. This usually wears off, but in extremes people may remain, as the jargon has it, “in denial”. Faced with overwhelming evidence that their partner is having an affair, their ability to rationalise goes into overdrive. They can find alternative explanations for lipstick marks, incriminating receipts and anything else that challenges their beliefs.
The drive to deny is powerful, and deniers show much more energy and creativity than those who simply accept the evidence without question. This means that a denier can often run intellectual rings around an uninformed believer. This has been the case since the first big denial movement, the Flat Earthers (or “Planists” as they prefer). In the 1840s, the great Planist Samuel Rowbotham, alias Parallax, published pamphlets detailing his scientific experiments with canals and cannonballs.  These consistently showed that the surface of the Earth was indeed flat and not curved. He gave many public lectures, and his manner was so gentle and reasonable, and his years of experiment so thorough, that he was utterly convincing.
Of course, anyone with a scientific background could challenge Rowbotham at his talks. But given the option of siding with a mocking and scornful challenger or the mild and pleasant Planist with his reams of evidence, audiences generally took Rowbotham’s side.
Denial may be motivated by religion, as with the Flat Earthers or anti-evolutionists. Or it may be simple self-interest, as it seems to be with climate change deniers. This is not necessarily cynical; psychological tests have shown that people are prone to believe whatever benefits them.  Many in the oil industry genuinely believe that global warming is a vile hoax. The motive may be more complex, as with the AIDS denial movement.
This movement is a medical conspiracy theory that AIDS is not due to the HIV virus (some even claim that AIDS is caused by anti-retroviral drugs used to treat HIV). The movement started in the mid-Eighties when the causes of the disease were mysterious and there were theories that it might be caused by amyl nitrites (a drug popular with the gay community) or other factors. The isolation of HIV and the development of effective antiviral therapy all but ended the debate in the West. However, in Africa there is a lingering mistrust of former colonial powers and drug companies, and AIDS denial continues.
Some AIDS deniers use scientific arguments, saying that HIV does not meet “Koch’s Postulates”, the three conditions required to prove that an agent is a cause of a disease. These state that the agent must be found in every patient with the disease, that it must be possible to isolate the agent and grow it in a pure culture, and that it must be possible to cause the disease in a healthy person using the agent. Technically, as only 99.975 per cent of AIDS sufferers have tested HIV-positive, the first postulate might not be true. And as HIV cannot be grown separately, it does not meet the second criterion – but then neither do influenza, smallpox nor measles.
In South Africa, President Theo Mbeki allowed denialists to decide policy. This decision was eventually reversed, but focusing on better nutrition for HIV patients rather than anti-retroviral drugs is believed to have cost some 356,000 lives in South Africa. 
The biggest current showdown is between the mainstream scientific establishments and “climate change deniers,” some of whom apparently have backing from industrial groups, in particular the oil companies. The approach is similar to that used by tobacco companies faced with evidence about the health risks of smoking. As with the Planists, they are not seeking to convince the scientists, but to persuade the public and political decision-makers that the scientists are wrong. They say that climate change reports are exaggerated, alarmist and driven by academics seeking to get more grant money and boost their own importance. 
A recent poll shows that only 53 per cent of Americans believe that global warming has had any effects, and 41 per cent believe that it is ‘exaggerated’.  This compares to about 96 per cent of climatologists who believe the effects are occurring…  but only 47 per cent of petroleum geologists. Believers say that it is vitally important for us to act on climate change now. Deniers may be seen as saboteurs bent on wrecking our only chance of saving the world. Their dangerous views may become as stigmatised as holocaust deniers.
And Fortean Times, rather than being seen as cosily eccentric, may start to be viewed as a breeding-ground for dangerous heresies…
1 Encyclopedia of Mental Disorders.
2 Complete text of his work “Zetetic Astronomy”.
3 Cognitive dissonance experiment.
4 New Scientist on Aids denial.
5 Newsweek on Climate change denial.
6 Gallup poll.
7 Poll of scientists.