Now and then, in just the right situations, there’s a lot to be said for intolerance—especially when it comes to the safety of kids. We don’t tolerate bullying in schools on the false belief that a few scuffles can build character. We don’t tolerate smoking on playgrounds because parents should have the right to determine the tobacco habits of their second-graders.

And we shouldn’t—but too often still do—tolerate parents who deny established science and refuse to vaccinate their school-age children, potentially endangering every other child in the school and the community beyond as well. That’s a lesson the families at Brunswick North West Primary School in Melbourne, Australia are learning in the worst way possible after as many as 80 of 320 students—or up to 25% of the student body—have been struck by chicken pox in just the past two weeks, thanks to the school’s liberal policies concerning vaccine refusers.

Get our Health Newsletter. Sign up to receive the latest health and science news, plus answers to wellness questions and expert tips. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Brunswick’s no-vax tolerance was not just an unwritten thing, but was formally stated in a newsletter distributed in May. “Staff respects the right of every family to make choices about immunisation and we will definitely not exclude children who are not fully immunised from our service,” said the text of the newsletter, according to the Victorian edition of the newspaper The Age. “We expect all community members to act respectfully and with tolerance when interacting with other parents and carers who may have a differing opinion to their own.”

The same newsletter conceded that the school’s vaccination rate was only 73.2%—far below the level needed to ensure herd immunity (generally over 90%), which protects the few people in any community who can’t be vaccinated for legitimate medical reasons. That made the school a target-rich opportunity for the chicken pox virus. Across the local postal code the vaccine rate is 92%; it’s a slightly lower 90.2 in the entire state of Victoria.

At least some of the children who got sick at Brunswick had actually received the chicken pox vaccine, which is admittedly not 100% effective. That fact gives cover to the anti-vax crowd, who point to such imperfect protection as evidence that vaccines are useless anyway. But something shy of 100% is still a huge majority of the entire vaccinated community, and kids who have gotten the shot and still get sick tend to come down with a mild case of the disease, developing, on average, only 25 of the telltale chicken pox spots, compared to 800 across much of the body for unvaccinated children.

Victoria, like a growing numbers of states and localities in the U.S., recently passed a law barring entry to day care for pre-schoolers who are not up to date on all their recommended vaccines, though the rule does not extend to grade schools. The new policy, which will go into effect on January 1, is dubbed “No Jab, No Play,” and there’s a nice, non-negotiable sound to that rule.

There may be all manner of great things about living in a big, brawling, pluralistic democracy like Australia or the U.S., but putting up with know-nothingism in the service of open-mindedness is not always one of them. If you want to believe climate change is a hoax or Roswell aliens faked the moon landings, fine. But other choices have different consequences.

They are the kinds of consequences that sickened the Brunswick school-children, who had no voice in the choice their parents made to leave them unprotected. They are the kinds of consequences, too, that were suffered by the family of Ottawa mom Tara Hills last spring, when all seven of her children came down with whooping cough, after she and her husband chose not to vaccinate them.

In a candid and courageous blog post on the site TheScientificParent.org, Hill described the uncertainty they felt in making their decision. “We stopped [vaccinating] because we were scared and didn’t know who to trust. Was the medical community just paid off puppets of a Big Pharma-Government-Media conspiracy? Were these vaccines even necessary in this day and age?”

They most certainly are necessary, as she found out, when she was confined to her home with her sickly brood for the full week it took them to get well. “I’m writing this from quarantine,” she began her post, “the irony of which isn’t lost on me.”

Merely ironic is the best way these kinds of avoidable outbreaks play out. Grave illness and even death is the worst. Tolerance is one of the greatest of human impulses—the social and intellectual flexibility that allows a society to function at all—but there are limits. There is no reason to tolerate a virus in our midst that could have been kept out. And there’s no reason to tolerate the kind of thinking that allowed it to get there.

Write to Jeffrey Kluger at jeffrey.kluger@time.com.