The uncertainty tactic is a frequently-used strategy by purveyors of all forms of woo. This tactic involves taking a widely-accepted scientific theory - such as evolution, anthropogenic global warming, peak oil, or the dangers of secondhand smoke - and contrasting the consensus view with a number of critics. Then the proposition is made that the truth is "uncertain" to a large degree, and so "both sides" should be taught.
 There are always critics
It is a sad truism that you can always find someone in a lab coat to disagree with the majority on any given issue. There are serious people who disagree with the consensus view on evolution, anthropogenic global warming, secondhand smoking, and so on. But there are actually also serious people who disagree about gravity, a constant speed of light, or continental drift. The crazier the theory, the fewer who believe. But when you throw in inducements like money, fame, or religion... the list of people willing to speak out gets a lot longer.
 The tactic in use
While this tactic was first notably used by Big Tobacco to protest that the "science was still out" on the dangers of smoking during the 1950s and 60s, the truly magnificent deployment of the uncertainty tactic is found in the "Teach the Controversy" push against evolution in American public schools by the Discovery Institute. As part of a broader plan, the Discovery Institute dredged up a variety of Christianity-inspired creationists with vaguely scientific underpinnings - and a few surprisingly capable and notable scientists - and carefully set about organizing their insurgency against evolution, intent on replacing it with "intelligent design."
By launching their own pseudojournals, writing books, and being as vocal as possible about intelligent design, the minions of the Discovery Institute attempted to project an aura of being more numerous than they really were. Petitions and demonstrations, joined in later years with such items as the film Expelled: No Intelligence Allowed, drummed up the notion that there was serious scientific disagreement about evolution... and accordingly that creationism should be taught in public schools as well.
As is usually the case, the antidote was a serious and patient and continual refutation. Tireless bloggers, columnists, and the good people at the National Center for Science Education have continued to defeat the Discovery Institute's gambit of the Uncertainty Tactic.