Science by its nature is contentious. Before a scientific hypothesis can be elevated to a theory, a solid body of empirical evidence must be accumulated and differing interpretations debated, often vigorously. But while spirited debate and skepticism of new ideas are intrinsic to the scientific method, stooping to personal hostility and ad hominem (against the person) attacks are an abuse of the discipline.

If the animosity were restricted to words alone, it could be excused as inevitable human tribalism. Loyalty to the tribe and conformity are much more highly valued than dissent or original thinking; ad hominem attacks are merely a defensive measure against proposals that threaten tribal unity. 

However, when the acrimony in scientific debate goes beyond verbal to physical abuse, either threatened or actual, then science itself is truly under assault. Unfortunately, such vicious behavior is becoming all too common.  

A recent example was a physical attack on pediatrician and California state senator Richard Pan, who had authored a bill to tighten a previous law allowing medical exemptions from vaccination for the state’s schoolchildren. After enduring vitriolic ad hominem attacks and multiple death threats calling for him to be “eradicated” or hung by a noose, Pan had to get a court restraining order against an anti-vaccinationist who forcefully shoved the lawmaker on a Sacramento city street in August, 2019, during debate on the exemptions bill. Although the attacker was arrested on suspicion of battery, Pan told the court he was fearful for his safety.

Pan has long drawn the anger of anti-vaccine advocates in California for his support of mandatory vaccination laws for children. But science is unquestionably on his side. Again and again, it’s been demonstrated that those U.S. states with lower exemption rates for vaccination enjoy lower levels of infectious disease. It’s this scientific evidence of the efficacy of immunization that has prompted many states to take a tougher stand on exemptions, and even to abolish nonmedical exemptions – for religious or philosophical reasons – altogether.

Medical exemptions are necessary for those children who can’t be vaccinated at all owing to conditions such as chemotherapy for cancer, immunosuppressive therapy for a transplant, or steroid therapy for asthma. Successful protection of a community from an infectious disease requires more than a certain percentage of the populace to be vaccinated against the disease – 94% in the case of measles, for example. Once this herd immunity condition has been met, viruses and bacteria can no longer spread, just as sheer numbers protect a herd of animals from predators.

But the earlier California law was being abused by some doctors, who were issuing exemptions that were not medically necessary at the request of anti-vaccine parents. The practice had caused the immunization rate for kindergarten-aged children to fall below 95% state-wide, and below 90% in several counties. As a result, measles was on the rise again in California.

Shortly after Pan’s bill was passed in September, 2019, another disturbing incident occurred in the legislature itself. An anti-vaccine activist hurled her menstrual cup containing human blood from a balcony onto the desks of state senators, dowsing several of the lawmakers. The woman, who yelled “That’s for the dead babies,” was subsequently arrested and faces multiple charges.

In the lead-up to such violence, the ad hominem attacks on Pan were no more virulent than those directed a century ago at Alfred Wegener, the German meteorologist who proposed the revolutionary theory of continental drift. Wegener was vehemently criticized by his peers because his theory threatened the geology establishment, which clung to the old consensus of rigidly fixed continents. One critic harshly dismissed his hypothesis as “footloose,” and geologists scorned what they called Wegener’s “delirious ravings” and other symptoms of “moving crust disease.” It wasn’t until the 1960s that continental drift theory was vindicated.

What’s worrying is the escalation of such defamatory rhetoric into violence. The intimidation of California legislators in the blood-throwing incident, together with the earlier street attack on Pan and death threats made to other senators, are a prime example. The anti-vaccinationists responsible are attacking both democracy and science.

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