Anti-vaccine activists stand outside a medical facility in Atlanta, Georgia - WARNING: Use of this copyright image is subject to the terms of use of BBC Pictures' Digital Picture

There may be no force on earth more powerful than the protective instincts of a parent. It can overcome almost any obstacle for good or ill – including logical thought and rational argument.

The Conspiracy Files: Vaccine Wars (BBC Two) exposed this phenomenon at its most dangerous, forensically pulling apart the anti-vaxxer movement with widely discredited concepts such as “facts” and “experts” until there was nothing left but opportunists, cranks and social-media bots using it to attack Big Government and Big Pharma.

Caught in the crossfire: angry, grief-stricken mothers and fathers trying to come to terms with their son or daughter’s condition. This was a battle of evidence against emotion, with no winners.

Victoria James’s excellent film painted a detailed picture of a conspiracy metastasising in the Fake News era. She interviewed people from all sides of the debate, from concerned scientists and government officials to parents and leaders of movements who allege links between childhood vaccinations and traumatic conditions such as autism.

That these parents had suffered dreadfully was not disputed, but a patchwork of anecdotal tragedies could never represent irrefutable proof. Their stance, at least, was defensible. Far worse were the likes of the disgraced and disbarred doctor Andrew Wakefield, a regular on InfoWars and producer of the derided, sensationalist “documentary” Vaxxed.

Among the hearsay and hysteria of the anti-vaxxers lay facts that were at best curious, at worst concerning. With American pharmaceutical companies not liable to pay compensation for vaccine-related injuries – the government has paid out after special court hearings since the Reagan era – where was their incentive to carry out safety tests of sufficient rigour?

Compulsory vaccination has recently been imposed in several American states. One was Maine, whose Representative Heidi Sampson opined: “Is the WHO a trusted source? I don’t know.” With wearying inevitability, the organisation was equated to Nazi Germany by more than one contributor (“I’m just saying, we gotta watch out”). Every parent should have the right to choose what’s best for their child, but with measles epidemics on the rise and those decisions having far-reaching consequences, should the greater good take priority?

Such ethical tightropes were, of course, immaterial for those populists exploiting the looming disaster, and adding vaccine scepticism to their growing arsenal of destabilising poison. The fact that this chilling account was broadcast on a pillar of the “mainstream media” will be enough to disqualify it for some; for the rest of us, it was as important as it was troubling.