My Twitter feed was filled this weekend with anger directed at parents who fail to vaccinate their children. The anger is justified, since these parents have fueled a resurgence of measles and other preventable diseases.

One of many striking aspects is the way that many educated parents buy into junk science, exemplified by false claims that vaccines cause autism. It’s sociologically interesting that so many otherwise well-informed people embrace crazy theories so readily-debunked after a few minutes of web-searching.

I tweeted about it, and got a surprisingly widespread response.

No one factor explains what’s happening. Many intentional non-vaccinators are simply free-riding on the herd immunity they hope is created by other people’s children. Such collective action problems provide the basic case for mandatory vaccination….

Parents of autistic children have disappointing specific experiences that lead them to distrust medical authority—not to mention Big Pharma. As I have noted before, when helping systems fail to show parents a human face, it’s hardly surprising that these parents themselves turn away. Some naturally embrace tight-knit communities of like-minded parents within which all sorts of beliefs reinforce powerful group identities, and vice-versa. Within these same communities we are powerfully drawn to information that reinforces our common group beliefs.

Thus does motivated reasoning flourish—whether it’s 9/11 or Obama trutherism, or believing that MMR vaccines bring widespread and mysterious side-effects associated with autism. Precisely the same conditions promote affinity fraud. It’s no accident that wildly speculative financial products are pitched on red-meat political cable news shows and at every assemblage of fringe political movements.

There is another irony, too, the extreme gullibility that arises from globalized mistrust.

Helaine Olen and I are writing a book on personal finance. As part of the writing, I have become fascinated by various financial scams such as the rip-off annuities sold to people at dinner seminars across the country. So many of these scams start with scary Powerpoint slides warning that Medicare will go bankrupt, that Social Security won’t be around. As people eat their rubber chicken, they hear that the Federal Reserve doesn’t want you to know budget deficits will crash the economy.

Such presentations scare the heck out of near-retirees who rightly worry that they will outlive their money. These also—quite intentionally–discredit the usual sources of information and authority. Once people buy into that generalized mistrust, they become easy prey for many garbage financial products.

Here and elsewhere, the wildly credulous and the wildly distrustful have more in common than one might think. Whether you are a 60-year-old buying an annuity, a poor single mom contemplating moving in with her boyfriend, or a parent pondering a vaccine, you are right to consider the possibilities. You are right to have your guard up, too.

Whether you trust too much or too little, the capacity for granular judgments is precisely what you’re ill-equipped to do. If that single mom distrusts all men, she’ll miss opportunities with trustworthy men. Ironically, she’ll probably also miss specific danger signs of those who can’t be trusted. Judith Levine’s lovely Ain’t No Trust: How Bosses, Boyfriends, and Bureaucrats Fail Low-Income Mothers and Why It Matters documents how women on welfare have powerful experiences that lead them to become distrustful of the assistance system (and much else besides). This distrust leads them to overlook real opportunities provided by welfare-to-work programs and related efforts.

If you blindly distrust Big Pharma, you’ll miss out on life-saving drugs or fail to vaccinate your kids. If you are overly credulous about Big Pharma, you will miss that they sell some genuinely wasteful or dangerous junk.

If you distrust everyone and everything in the financial world, you may hide your cash in a mattress. You may also end up investing with some persuasive charlatan rather than with some reasonable mutual fund. Every day, people trust the wrong advice. Blind trust or distrust—and sometimes a combination of both– isolates people from readily-available critical information, making them easy prey for fraud.

We all have to live in the world, with our eyes open, ready to take a calculated risk knowing the possibility exists that our trust will be misplaced. If you’re too cynical to do that, you’ll find world of trouble. Ironically, you’re also an easy mark.

[Cross-posted at The Reality-Based Community]

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Harold Pollack

Harold Pollack is the Helen Ross Professor at the School of Social Service Administration at the University of Chicago.