I remember one especially long, anguished and beer-soaked argument about vaccination, in a pub in Leytonstone, East London, at some point in the middle of the last century.
A friend of a friend, mother of two small children, smart and funny, she was determined that her kids would not be getting the MMR (meales/mumps/rubella) jab.
She'd seen the evidence linking it with autism, it was there all over the internet, and she had a cousin, I think it was, whose child had developed autism after getting the vaccination.
Misinformation, scare-mongering and nonsense, I harrumphed. I pulled out my Blackberry - this was a while ago, yes - and loaded up pages of authoritative analysis that utterly invalidated Dr Andrew Wakefield's study that purported to show a link between the vaccination and autism.
She had been taken in by pseudoscience that had bloated into a conspiracy theory, and a deeply dangerous one, too, for the health of children everywhere.
She wasn't having any of it, and not only because I was almost certainly guilty of obnoxious mansplaining (before it was cool). Her conviction, I think, was that even a faint possibility that the claimed link existed was enough to dissuade her from vaccination.
Informed by copious ruminations and anecdata online, bolstered by the terrifying headlines in the mass-market, insidious, fear-tapping newspaper the Daily Mail - one of the most poisonous influences, in my opinion, on British life - she just wasn't going to hazard any risk.
We were, after all, talking about her children, and one of the most hard-wired instincts of a parent is to obviate risk.
I understand this better now I have children of my own: to sign consent for your child to go under a general anaesthetic, for example, is a momentary torment, no matter how clearly you've grasped the minuscule scale of that risk.
The utterly invalidated Dr Andrew Wakefield has emerged out of the shadows in recent months, as the director and star of Vaxxed: From Cover-Up to Catastrophe, a self-described "emotive" film that rehashes the utterly invalidated theories he propounded all those years ago.
Actually, he no longer gets the "Dr" honorific: not that you'd know that from watching the film.
For some reason it reportedly omits to mention that Wakefield was in 2010 found guilty of serious professional misconduct and struck off the medical register by Britain's General Medical Council.
His studies on children had "brought the medical profession into disrepute". He had "abused his position of trust".
There were "multiple separate instances of serious professional misconduct".
Three months earlier, the Lancet, which published the discredited, inestimably damaging paper by Wakefield in 1998, formally retracted it. Wakefield had "deceived the journal", said the editor, Richard Horton.
It was clear, "without any ambiguity at all, that the statements in the paper were utterly false."
A 2011 editorial in the British Medical Journal declared Wakefield's paper an "elaborate fraud", crediting the dogged reporting of Sunday Times journalist Brian Deer in exposing it.
Wakefield's mendacity, "fuelled by unbalanced media reporting and an ineffective response from government, researchers, journals, and the medical profession" had markedly damaged the fight against infectious diseases, the editors concluded.
"But perhaps as important as the scare's effect on infectious disease is the energy, emotion, and money that have been diverted away from efforts to understand the real causes of autism and how to help children and families who live with it."
This is the backdrop against which to view the intervention of Dr Lance O'Sullivan, who leapt on stage ahead of a screening of Vaxxed in Northland this week, to condemn the film.
"This idea of anti-immunisation has killed children around the world and actually will continue to kill children," he said. It was "misinformation based on lies, quite frankly".
O'Sullivan, a former New Zealander of the Year, has a visceral and emotional response, too - he describes having held in his arms babies whose lives could hinge on widespread vaccination.
O'Sullivan's emotion, however, stems out of an understanding of a body of reputable evidence, which shows the unmistakable effectiveness of vaccination in eradicating disease.
It shows, too, that to be properly effective, and to protect those too young or sick to be immunised, a society needs to achieve "herd immunity", usually around 95% of the population.
The science is not controversial: refusing to vaccinate your own child could imperil the life of a newborn, or a child with cancer.
In taking his stance, O'Sullivan has faced waves of attacks and threats from the anti-vaccination lobby, including slanders related to his disabled son. A similar pattern is played out across the internet.
Comments posted on Facebook are sometimes literally sickening. God knows this territory is raw for parents, those whose lives have been turned upside down by autism especially.
But if you're contemplating seeing Vaxxed, please first read about the man behind it, Andrew Wakefield, and read media of repute, rather than in the undergrowth.
Because his work is not some courageous journalistic endeavour; it is fear-preying, flat-earth propaganda.