The latest bit of life-threatening trivia that's seen some major media coverage has been the fear of a link between vaccines and autism. Such a link does not exist. The science is there, is solid, and is not an evil plot. So why does the myth persist? As the linked-to story in Wired says, parents are willing to do anything out of love for their children. They are eager and willing to believe in alternative cures, or in radical measures to save their children. A lot of emphasis has been places on this as a failure of rationale choice: vaccines are inherently safer than the diseases they protect against. A striking visual example is this chart discussing the risk of taking the HPV vaccine versus the risk of not doing so. HPV not in any way associated with Autism, but the case against HPV is similar: well-publicized incident of a side effect gone wrong, or of the potential for a harmful side-effect, with little real coverage of the damage caused by not taking the vaccine. To scientists (and, generally, to rational human beings) this makes no sense: the least risky action is desired, and should be taken.
So why the resistance to vaccinations? Agency.
People see themselves as having control over whether or not to get a vaccination; they are upset at laws about mandatory vaccinations, which to them imposes the risk of side effects. In refusing to be vaccinated or vaccinate their own children, this people are acting against the only risk they perceive: that caused by vaccines themselves.
They are, at the same time, assuming that disease is a factor beyond their control. Getting infected by any of the diseases that a vaccine would protect against is seen as something against which they are powerless (or, more likely, unaware), and so isn't a risk to avoid. They've seen/read/researched the stories about things gone terribly wrong with vaccines. But the renewed outbreak of diseases like measles (basically non-existent for my generation and the one immediately preceding it) doesn't register as a new risk. These people, these parents fearful of autism (or more generally the mercury in all vaccines) are making a terrible assessment of the possible risks, but it's not irrational - they just have no idea of the risks where the balance of risk falls.
Most relevantly, they don't see getting vaccinated as reducing risk. Because exposure to disease isn't something they have control over, but exposure to medicine totally is. It's a major disconnect they've developed between vaccinations and disease. The solution? Coming from my social-sciencey background, I'm inclined to think that the problem can be solved by a reframing of vaccination. Vaccinating is a choice just as much as not vaccinating is, and the positive good caused by vaccines is little publicized, and even more rarely seen as an actual decision.
We humans remember when things go wrong. We have a terrible problem with forgetting when and why things went right.