People have a right to be ignorant. Just as we can choose to damage our health by overeating, smoking cigarettes, and neglecting to take prescribed medications, we can also choose to remain uninformed on policy issues.Perhaps ignorance makes sense sometimes. According to economists, "rational ignorance” comes into play when the cost of gaining enough understanding of an issue to make an informed decision relating to it outweighs the benefit that one could reasonably expect from doing so. For example, many who are preoccupied with family, school, work, and mortgages may not consider it cost-effective to sift through a mass of often-inconsistent data to understand, say, the risks and benefits of nuclear power, plasticizers in children’s toys, or the Mediterranean diet.The deluge of conflicting data relating to various foods’ costs and benefits exemplifies the challenge inherent in making informed decisions. In a recent study, Jonathan Schoenfeld and John Ioannidis found that, despite the media hype, "scientific” claims that various foods cause or protect against cancer are frequently not supported by meta-analysis (analysis of pooled results from multiple studies). As Ioannidis put it, "People get scared or they think that they should change their lives and make big decisions, and then things get refuted very quickly.”People are particularly likely to exercise their right to ignorance – rational or not – when it comes to issues of science and technology. A 2001 study sponsored by the US National Science Foundation found that roughly half of people surveyed understood that the earth circles the sun once a year, 45% could give an "acceptable definition” for DNA, and only 22% understood what a molecule was.In 1995, the cosmologist Carl Sagan expressed concern about the trend toward a society in which, "clutching our crystals and religiously consulting our horoscopes, our critical faculties in steep decline…we slide, almost without noticing, into superstition and darkness.” More recently, British polymath Dick Taverne warned that, "in the practice of medicine, popular approaches to farming and food, policies to reduce hunger and disease, and many other practical issues, there is an undercurrent of irrationality that threatens science-dependent progress, and even the civilized basis of our democracy.”Indeed, while people are entitled to believe in horoscopes, trust in crystals to bring good luck, or buy into quack medicine, such "junk science” becomes a serious threat to society when it is allowed to influence public policy. Consider, for example, the response last year by some activists in Key West, Florida, to efforts aimed at stemming the spread of dengue fever, a serious, potentially life-threatening disease, which reappeared in the area in 2009 after being absent for more than 70 years.Using genetic-engineering techniques, the British company Oxitec has created new varieties of the mosquito species that transmit dengue fever. The new mosquitos contain a gene that produces high levels of a protein that stops their cells from functioning normally, ultimately killing them. As long as the modified male mosquitos are fed a special diet, the protein does not affect them. When released, they survive just long enough to mate with wild females, passing along the protein-producing gene, which kills their offspring before they reach maturity – resulting in the species’ elimination after a few generations.After receiving the needed approvals, Oxitec worked with local scientists to release the modified mosquitos in the Cayman Islands and in the Juazeiro region of Brazil. According to the published accounts of these experimental releases, the approach was highly effective, reducing the infected mosquito population by 80% in the Cayman Islands and by 90% in Brazil. The company is awaiting approval from Brazil’s health ministry to implement this approach as a dengue-control policy.While similar releases in Florida are years away, some locals have already reacted forcefully. One activist gathered 100,000 signatures on a petition to oppose using the mosquitoes in eradication efforts. But her concerns – "What if these mosquitoes bite my boys or my dogs? What will they do to the ecosystem?” – have no scientific basis, and thus reflect voluntary ignorance. With a little research, she would have discovered that male mosquitoes do not bite, and that the released mosquitoes (all male) die in the absence of their specially supplemented diet.In fact, the experimental releases revealed no detectable adverse effects of any kind. But presenting the facts in a reasonable manner, as Florida mosquito-control authorities have attempted to do, has not been enough to change opponents’ minds. Unfortunately, those who choose ignorance are immune to – or simply prefer to ignore – reason.Why are so many people afraid of so many things? Cancer epidemiologist Geoffrey Kabat identifies several factors, including "the success of the environmental movement; a deep-seated distrust of industry; the public’s insatiable appetite for stories related to health, which the media duly cater to; and – not least – the striking expansion of the fields of epidemiology and environmental health sciences and their burgeoning literature.”Regardless of their reasoning, people have a right to choose ignorance. But allowing that choice to drive public policy constitutes a serious threat to scientific, social, and economic development.Henry I. Miller, a physician and fellow in Scientific Philosophy and Public Policy at Stanford University’s Hoover InstitutionCopyright: Project-syndicate.org