“Actions have consequences,” as the saying goes. Inaction, by contrast, is a mostly neutral state of being—or so it often seems in our mind’s eye.

We are, in fact, predisposed to think that harms that result from our actions are worse than those that arise from our inaction. Sins of the first variety can whisk us into “Thou shall not” territory. Sins of the second, we tend to think, are crimes of mere idleness, laziness, or thoughtlessness at worst.

That bifurcation is deeply ingrained in the human psyche—and it can get us into big trouble. As Ilana Ritov and Jonathan Baron have shown in various research studies, such “omission bias”—the instinctive belief that doing something is inherently riskier than doing nothing—can often lead to the far greater harm.

I thought of this (and of my old interviews with Baron, a professor of psychology at the University of Pennsylvania) as I read through a 104-page report on public attitudes about vaccines (and about trust in medical science in general), which is being released today by the Pew Research Center.

The report drives to the heart of what, quite astoundingly, has become a matter of emotional public debate in recent years: whether or not vaccines are safe. And while the Pew found that an overwhelming majority of U.S. adults (82%) say that vaccinating healthy children against measles, mumps, and rubella ought to be a requirement for attending school, there is still a frighteningly plump wedge of Americans (17%) who believe that vaccination should be optional. (The share of those with children under the age of five who believe the latter is even higher, at 22%.)

Such doubt over vaccine safety and even over the necessity of these inoculations—a viral holdover from a now-retracted 1998 Lancet study that claimed a possible link between the MMR vaccine and autism—has become endemic in America. President Trump raised the issue during his campaign and stoked additional speculation over his views in the days soon after the election—causing public health experts to worry that one of the great bulwarks against the spread of infectious disease in the U.S. may soon crumble. (Rebecca Robbins at STAT had a lovely piece on this on Tuesday.)

I won’t belabor the old fact-based arguments when it comes to vaccine safety and, importantly, public safety. The CDC, the American Academy of Pediatrics, and many, many others have done that already.

But the bottom line is that failing to vaccinate our kids against serious and preventable illnesses is itself a serious and preventable mistake. Inaction has consequences too.