On CBS's Face the Nation last Sunday, Tom Frieden, the director of the Centers for Disease Control and Prevention, said he is "very concerned" about the possibility of a massive, sustained outbreak of measles in the United States. A growing number of parents are deciding not to vaccinate their children, resulting in 100 cases of measles in 14 states in the latest outbreak. Frieden argued that it is extremely important to prevent measles from re-establishing itself as an endemic disease, after it was eradicated at great expense and effort around the year 2000.

New Jersey Gov. Chris Christie (R) chose the very next day to downplay the threat, a reply of sorts to President Obama, who strenuously recommended vaccination in an interview. At a press conference in England, part of a trip that is widely considered to be a rehearsal for a presidential run, Christie said that while he has vaccinated his own children, he did not expressly recommend vaccination for others. Instead, people "should have some measure of choice." (The libertarian Sen. Rand Paul (R-Ky.) went further, saying of vaccines, "Most of them ought to be voluntary.")

After criticism, Christie amended his statement to emphasize that "there is no question kids should be vaccinated," while still maintaining that the danger of vaccine-preventable illnesses should be "balanced" against the supposed risks of vaccines. But it still doesn't wash, given the 2009 letter he wrote saying he would "stand with" vaccine-refusenik parents.

Christie is utterly mistaken on the science. But his comments exemplify a typically American selfishness, one that in this case is not just morally odious, but incoherent.

It's true that an individual case of measles is a lot less threatening than one of Ebola, for which Christie — again acting against the best advice of medical scientists — last year briefly enacted a forcible quarantine for health-care workers who had treated Ebola in Africa. By this reasoning, it is worth curtailing individual liberty for very deadly diseases, but not so with less dangerous ones.

But just because a disease is not as bad as Ebola does not mean it isn't still worth eradicating. Furthermore, the measles vaccine is extremely safe for healthy people: though there is a tiny risk, as there is with every activity, it is far smaller than getting measles itself. Only the very young, and those with compromised immune systems or allergies, have an actual reason to avoid it.

And make no mistake, measles is still a very serious illness. A quarter-million people worldwide got it last year, mostly children in the developing world; more than half died (though that death rate can be reduced to about 1 to 2 out of 1,000 with modern medicine). Long-term complications can include deafness, pneumonia, encephalitis, and a degenerative nerve disease. It's also incredibly contagious, "probably the most contagious infectious disease known to mankind," as a CDC specialist told NPR. Back in the pre-vaccine days, each person who caught it infected 17 new ones — as opposed to less than two for Ebola.

More broadly, this entire argumentative frame misses the greatest benefit of vaccines: herd immunity. A population vaccinated to a high enough level becomes largely impervious to the disease by sheer statistics, and that protects the vulnerable ones who can't be vaccinated, or those whose vaccines didn't take root. Vaccines are not just about preventing personal illness, but stopping them from spreading. Done systematically enough, it can eradicate diseases completely. The elimination of smallpox, which killed something like 300 million people in the 20th century alone, ranks high on the list of human accomplishments.

That is why this is as much a moral issue as a scientific one. The appalling selfishness inherent in the idea of "vaccine choice" was starkly illustrated in a recent CNN story. After the measles outbreak at Disneyland, CNN talked to a family whose 10-month-old baby had contracted the disease. They're terrified he'll pass it on to their 3-year-old daughter, who has leukemia and can't get the vaccine — but might be killed by the disease. Here's the response of a refusenik parent:

CNN asked Wolfson if he could live with himself if his unvaccinated child got another child gravely ill. "I could live with myself easily," he said. "It's an unfortunate thing that people die, but people die. I'm not going to put my child at risk to save another child." [CNN]

In other words, it's okay to cause the death of another child if your kid wants to go to Disneyland. And that's leaving aside the risk to Wolfson's own kids, who are put at risk by his atrocious parenting.

Every person depends on society to function. From public roads to sanitation to clean water to the very economic system itself — your day is made possible by millions of other people doing their small part to maintain our civilization. When it comes to violently contagious diseases, it is not possible to speak meaningfully of choice divorced from the needs of those people.

Herd immunity, like many of the great public goods, is literally an issue of life and death. As such, Christie's parental "choice" is a gross infringement of others' basic rights.