It's all over social media — the posts calling parents "dumb" or even "criminal" for failing to vaccinate their kids against measles.
But could the heated public discussion about vaccines in fact lower vaccination rates?
While a little social pressure is good, experts who have studied the psychology of the vaccine doubters say it's counterproductive to be accusatory — or even to try provide a little well-meaning education.
"When you attack somebody's values, they get defensive," said risk communication expert David Ropeik. "It triggers an instinctive defensiveness that certainly doesn't change the mind of the vaccine-hesistant person."
And some of the criticism on cable television, social media and in mainstream newspapers and magazines is starting to look like bullying, Ropeik and other experts said.
"When they get defensive they carry their campaign more fervently, and that has the chance of poisoning other people," said Ropeik.
"There are millions of people who are ambivalent to some degree. When they hear the people being picked on defend their views, that has the real prospect of turning some of those people against vaccines."
The anti-vaccine movement is nothing new. People have been questioning the safety and efficacy of vaccines for decades, especially once the illnesses the vaccines protect against started to disappear, and the risks of the vaccine began to loom larger when there was no backdrop of death and disease.
This time, it's different, said Ropeik. At least 102 cases have been reported in the outbreak — 59 of them with a definite link to Disneyland. "The fact that this has happened in Disneyland has set off media attention unlike any previous outbreak," Ropeik said.
"This time the media is going, 'Aaah, measles.' It's louder than before because of Disneyland."
That extensive coverage means in turn that both vaccine-ambivalent parents and their critics are getting a lot of attention.
Dr. Gary Freed at University of Michigan said it makes for a teachable moment.
"The rates of vaccination have been falling," said Freed. As a result, there have been outbreaks of measles, mumps and whooping cough. "But it took the Disneyland episode to, I think, raise public awareness and consciousness to just how serious this is for the average child who becomes at risk as a result of other parents not vaccinating their children," said Freed.
But simply telling people their views are stupid, or even not fully informed, will not work, said Dr. Brendan Nyhan of Dartmouth University.
"It could make the problem worse. Imagine what calling people selfish and dumb can do," Nyhan said. "If people call me selfish and dumb, it doesn't make me more open-minded, and I don't know why anyone would think otherwise in this case. I think it's really short-sighted. People enjoy lashing out at anti-vaccine folks, (but) it turns into an 'us versus them' thing."
Nyhan conducted a study last year with Freed that found that when they gave ambivalent parents facts that show vaccines do not cause autism, they were even less likely to vaccinate their kids than they were before.
"They are committed to that point of view. You can provoke a kind of backlash reaction if you are not careful," Nyhan said. "That is why it is important to test the messages that we use and avoid the counterproductive type of messaging seen in the wake of Disney."
Telling people they are wrong will just make them dig in their heels, said Nyhan.
"There is a psychological tendency called disconfirmation bias. Information we don't want to hear, we try very hard to reject it. That is especially true for beliefs that are central to our identity," he said.
Most Americans support vaccination. A survey from the Pew Research Center published last week found that 68 percent of American adults believe that vaccinations of children should be required, while 30 percent say that parents should be able to decide not to vaccinate their kids.
But groups such as the National Vaccine Information Center view and position themselves as courageous visionaries who challenge a flawed, mainstream point of view. Libertarian leaders such as Sen. Rand Paul, R-Ky., are taking on the issue of vaccination as a question of personal freedom.
It's becoming a political debate. New Jersey Gov. Chris Christie backed off remarks that suggested parents should have a choice in deciding whether to vaccinate, and former Secretary of State and first lady Hillary Clinton tweeted: "The science is clear. The Earth is round, the sky is blue and #vaccineswork."
Freed, Nyhan and Ropeik all agree that there will always be a core of people who question the science.
"I think we have to remember that there are a certain group of parents who, no matter what the evidence is, will decide not to vaccinate their children," Freed said. Some happen to be celebrities.
"However we must realize that shrill voices are not necessarily the most common voices. And although there may some significant push back in some quarters of social media, that doesn't mean that the increasing reality of the danger of non-vaccination isn't reaching some of the hesitant parents right now. There will always be shrill voices against immunization."
Freed said it's most important to ensure that discussion about the Disneyland measles outbreak doesn't turn into a debate about vaccine safety. In that context, he said, it's OK to apply a little gentle pressure.
"I think it's fair to make them feel social pressure that they may not be doing the best thing for their child or the best thing for their communities," Freed said. "We need to work to make the dominant paradigm one of the protection of children through immunization — the socially accepted choice, the morally accepted choice and the scientifically prudent choice."
Ropeik said all the news coverage could turn some parents more strongly pro-vaccine. Many parents and even pediatricians are not old enough to remember when measles was common and killed up to 500 people every year, mostly through complications such as pneumonia and encephalitis.
"This has always been an issue of risk versus benefit. Why should they take the small risk of the vaccine if the disease isn't around?" Ropeik said. "Some parents may become more afraid of the disease than the vaccine."
Coverage of the potential damage done by failure to vaccinate may also help the public health officials who want to improve vaccination rates, added Ropeik.
"The fact that these parents are being so vilified will make it easier for states and cities to make it harder to opt out," he said.