Vaccine deniers span all sides of the political fringe, to the peril of everyone else.

It’s grotesque, but not surprising, that in the midst of the current measles outbreak, some leading Republicans are humoring vaccine denialists. It is a near-perfect illustration of the craziness gap in American politics.

Vaccine skepticism is one of those issues, like 9/11 Trutherism, where parts of the fringe right and fringe left, each driven by their own fears about authority, curve around and meet each other. Yet only the fringe right is indulged by mainstream politicians.

There is a popular perception that vaccine refusal is driven by the sort of affluent, vaguely left-wing parents satirized by the Los Feliz Day Care Twitter feed. (“Vax or no vax,” one tweet reads, “none of our kids had measles, and we only went to Disneyland to protest commercialism and the anthropomorphization of animals.”)

But susceptibility to misinformation about vaccines is less about politics than about paranoia, and paranoia operates in many different cultural milieus. A recent paper by Yale Law School’s Dan M. Kahan found that perception of “vaccine risks displayed only a small relationship with left-right political outlooks,” though it is slightly more common on the right.

“Respondents formed more negative assessments of the risk and benefits of childhood vaccines as they became more conservative,” it stated.

A minimally responsible Republican Party would not pander to this sort of thing. But that is not what we have. Instead we have New Jersey Gov. Chris Christie answering a question about measles immunization by saying parents “need to have some measure of choice,” and that “not every vaccine is created equal, and not every disease type is as great a public health threat as others.” (After an uproar in the media, he backed away from this formulation, calling the scientific support for vaccination “pretty indisputable.”)

U.S. Sen. Rand Paul, R-Kentucky, described vaccine rejection as a freedom issue. On CNBC, he promoted the long-discredited link between vaccines and autism: “I have heard of many tragic cases of walking, talking normal children who wound up with profound mental disorders after vaccines.”

Democrats have shown much less fear of enraging the fever swamps. “The science is clear: The earth is round, the sky is blue, and #vaccineswork,” tweeted Hillary Clinton.

Speaking to The New York Times, former DNC Chair Howard Dean poured scorn on “entitled people who don’t want to put any poison in their kids and view this as poison, which is ignorance more than anything else.” So while hippie anti-vaxxers exist, they have essentially no political influence.

The craziness gap has real public health consequences. If vaccine denialism becomes subsumed into the culture war – and thus turns into another badge of political identity, like owning a gun, watching Fox News or rejecting evolution – it’s likely to increase. When Republicans can’t even stand up for something as simple as the easy prevention of deadly diseases, it leaves us all more exposed.

MICHELLE GOLDBERG is a senior contributing writer at The Nation.