Unfortunately, trial and error may turn out to be the best we've got

Megan writes:

A couple of days ago, Glenn Reynolds linked to an article he wrote in August on vaccines. As longtime readers know, this is a particular cause of mine; parents who don't vaccinate their children are able to do so only because most parents do vaccinate theirs. (No, really, I promise--if there were polio running around wild, as there would be if all parents acted like the anti-vaccinationists--then the people taking "personal belief" exemptions would almost all be lining up at the doctor's office begging to her to give little Tinkerbell the magic shot).

But there's a deeper point to be made about how the human brain, and society, treats risk:

Of course it is the very success of modern vaccines that makes this complacency possible. In previous generations, when epidemic disease swept through schools and neighborhoods, it was easy to persuade parents that the small risks associated with vaccination were worth it. When those epidemics stopped--because of widespread vaccinations--it became easy to forget that we still live in a dangerous world. It happens all the time: University of Tennessee law professor Gregory Stein examined the relation between building codes and accidents since the infamous 1911 Triangle Shirtwaist factory fire in New York and discovered a pattern: accident followed by a period of tightened regulations, followed by a gradual slackening of oversight until the next accident. It often takes a dramatic event to focus our minds.

...
The problem is that it simply won't do to say that we ought to be institutionally risk averse. All of these arguments could be applied just as well to gay marriage or abortion law or universal health care, if you lean that way--it's no good just saying that it hasn't hurt Sweden, because the deluge might still await.

Libertarians, conservatives, and progressives all need a better metric for distinguishing between the areas where we're improving on problems, and areas where we're simply eating our institutional and cultural seed corn. Unfortunately, trial and error may turn out to be the best we've got.