Fellow ScienceBlogger Tara Smith has a required reading article in PLoS Medicine on HIV denialists:
Since the ideas proposed by deniers do not meet rigorous scientific standards, they cannot hope to compete against the mainstream theories. They cannot raise the level of their beliefs up to the standards of mainstream science; therefore they attempt to lower the status of the denied science down to the level of religious faith, characterizing scientific consensus as scientific dogma . As one HIV denier quoted in Maggiore’s book  remarked, “There is classical science, the way it’s supposed to work, and then there’s religion. I regained my sanity when I realized that AIDS science was a religious discourse. The one thing I will go to my grave not understanding is why everyone was so quick to accept everything the government said as truth. Especially the central myth: the cause of AIDS is known.”
Others suggest that the entire spectrum of modern medicine is a religion .
Deniers also paint themselves as skeptics working to break down a misguided and deeply rooted belief. They argue that when mainstream scientists speak out against the scientific “orthodoxy,” they are persecuted and dismissed. For example, HIV deniers make much of the demise of Peter Duesberg’s career, claiming that when he began speaking out against HIV as the cause of AIDS, he was “ignored and discredited” because of his dissidence . South African President Mbeki went even further, stating: “In an earlier period in human history, these [dissidents] would be heretics that would be burnt at the stake!” .
HIV deniers accuse scientists of quashing dissent regarding the cause of AIDS, and not allowing so-called “alternative” theories to be heard. However, this claim could be applied to any well-established scientific theory that is being challenged by politically motivated pseudoscientific notions–for example, creationist challenges to evolution. Further, as HIV denial can plausibly reduce compliance with safe sex practices and anti-HIV drugs, potentially costing lives, this motivates the scientific and health care communities to exclude HIV denial from any public forum. (As one editorial has bluntly phrased it, HIV denial is “deadly quackery”) . Because HIV denial is not scientifically legitimate, such exclusion is justified, but it further fuels the deniers’ claims of oppression.
Read the whole thing.
I think that this hits on an important point. The common theme among scientific denialists is not the denial of particular scientific propositions. An individual that denies the validity of a particular scientific model can be confronted with evidence, and solution is reached.
Scientific denialists have the common theme of denying the legitimacy of the scientific process generally — usually by casting science as a flawed social system.
The only logical response the denial of the validity of the scientific enterprise as a whole is assertions that defend science generally. We may have been shooting ourselves in the foot thus far because we have confronted denial with facts related the the specific statement they were denying. For example, when people argue that mercury causes autism, we respond that there is no evidence for this statement. We talk about autism. Unfortunately, deniers are denying the whole shabang, the entire scientific process. In addition, to defending statements about autism, we need to start defending the whole shabang.
Scientists are indeed a social group, and as a consequence they suffer the same dangers of social groups such as group think. But I would ask the deniers what alternative means of systematically investigating reality they would prefer? They consider science tantamount to the investigation of reality by seance, but how would they organize it differently to remedy these defects?
Science is not perfect, but no better system for sifting through truth and non-truth has been devised. We need to start defending the system as a whole.