It happens approximately once a month. My email inbox, Facebook page, and whatever other form of electronic communication to which I have access gets slammed with denials of actual science. It usually comes from all sides - the right-wing people I know claim that "science proves" that homosexuality is evil and that global temperatures are either not changing or are simply natural and not anthropogenic, and the left-wing people I know claim that vaccines are evil and that all medical advances are actually part of some evil scheme on the part of Merck.
It's interesting to me that the groups who send these types of things don't really overlap, at least among the circle of people that I know, and that they take pot-shots at each other that could be charitably referred to as "the pot calling the kettle black." They point to the unscientific, pseudo-scientific, and anti-scientific claims of the others, while engaging int he same sort of behaviors themselves.
There are many issues that are publicly controversial, but well settled in the scientific community. Evolution does occur. The Earth is getting warmer, and it is probably anthropogenic. It is statistically far safer to be vaccinated against communicable childhood illnesses than not to be (and vaccines don't cause autism). Tobacco is a contributing factor to cancer. Many religious experience can be explained by brain functions. And so on and so forth. The problem is that every side can haul out a group of scientists, most politically motivated but some not, who will muddy the waters with "evidence" that doesn't actually stand up to scrutiny. Remember, the Tobacco companies still have scientists on staff that claim that cigarettes can not be linked to lung cancer - it is naive to think that your particular pet cause is any less prone to corruption.
Don't get me wrong, I think that people who are in denial of scientific truths are not doing so out of malice. Most of these people are simply doing what we humans do. We all have a narrative that links our beliefs together, and we wall tend to dismiss information that doesn't jive with our narratives. Increasingly our narratives are political, and unfortunately this means that many, in fact most, of us have conflated political thinking with critical thinking.
For example, every person that I personally know who believes that global warming is not occurring buys into a political ideology in which they are opposed to regulation. The need to limit carbon emissions will result in further regulation, which they have a visceral reaction to, and as a result they reject the scientific claims that would justify a political action that they dislike. It's the confirmation bias in action. Indeed, it is common to hear people claim that "global warming is just a tool for people in power to gain more control over our lives" without ever addressing the actual data. This position gains a veneer of credibility when scientists who have either financial or ideological motivations muddy the water and provide questionable or misleading evidence to support the contention of this side (listen here for a good discussion of this).
Likewise, I know many people who are worried over the influences that large corporations have on politics and society. These are well-founded concerns, but most of these folks tend to adopt an anti-corporate political narrative in which any claim that puts corporation in a bad light is accepted, and any evidence that counteracts such claims is denied. So, it's common for me to hear about how vaccines are a source of suffering and part of a "big pharma conspiracy" when the evidence pretty conclusively shows that they are a boon. The claim of the malfeasance of large pharmaceutical corporations (who, it should be said, DO engage in some crappy activities) fits the narrative, so claims consistent with this are accepted while evidence opposing it is ignored. Confirmation bias, again. And, again, there are scientists with either ideological or monetary interests who are perfectly willing to put shaky or false evidence into the public debate.
Adding even further to the problem is that people are increasingly getting their news and other information from sources that are more interested in pushing a political and/or ideological agenda than in actually informing their audience. Simply put, if you are using as evidence information gathered from Glenn Beck, Rush Limbaugh, the Huffington Post, James Inhoffe, the RNC, the DNC, Michael Moore, etc. etc., then you are being misinformed. All of these sources, and many more besides, have a particular agenda that does not have your or my best interests at heart, though all of them (and their followers) will claim otherwise.
It boils down to this. The following are empirical questions: Is the Earth's climate changing, and is it anthropogenic; does evolution occur; are homosexuals deviants or simply part of normal human variation; are vaccines safe and effective; does tobacco cause lung cancer; does gun ownership reduce crimes; could the World Trade Center have been toppled by the airliner; and we can think of many other politically controversial claims that are nonetheless at their base empirical claims. And empirical claims can only be resolved by empirical evidence. If there is reason to question particular pieces of evidence, then it is fair to examine the interests of the producers of that particular evidence (unfortunately, with the proliferation of think tanks, and the increasing profits to be had from public intellectuals working the outrage of particular groups, questionable evidence is common in the publci arena). However, when political your side's political interests and narratives are your first line of argument on an empirical question, you are not thinking critically, you are thinking politically, and you are probably being taken for a ride.