Play the footage of the 1969 moon landings back slowly, and for a split-second you may see a grey blur at the top of the picture. That’s the cameraman’s sound boom accidentally straying into shot, proving beyond doubt the whole thing was really filmed in Pinewood studios. We never went to the moon. And but for a rookie error that somehow got past the editing suite, we’d never have known.

Or so my friend’s grandfather steadfastly maintained, which as kids we obviously found hilarious. But conspiracy theories are no longer so funny, or so innocent.

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The comedian Rufus Hound has 1.2 million followers on Twitter. That’s more than double the circulation of a national broadsheet newspaper – although, crucially, minus the journalistic and regulatory processes that might stop a broadsheet idly speculating that Theresa May allowed 22 people to be murdered in Manchester this week just to stop her poll lead sliding.

This week Hound shared with his followers a tweet from someone in Leicestershire arguing that “given that the attacker was known to MI5, the timing seems fortunate for May that an attack ‘slips through’ as Labour making progress”, adding for good measure: “Apologies for mild tinhattedness, but I’ve been thinking the same. Esp. as she was Home Secretary for so long. #reichstagFire”

This isn’t just silliness crowned with ill-judged Nazi references. It’s using a public platform to baselessly suggest that loved ones could be alive today had the Tories not been desperate to win an election. Before eventually apologising and deleting the exchange, Hound explained that “I struggle believing our establishment is incapable of great evil” – as if one comedian’s struggle with his own addled beliefs was reason enough to allege complicity in mass murder. And if you’re thinking that it doesn’t matter much because nobody believes this nonsense, don’t bank on it.

Social media is littered with amateur “truthers” who once watched a YouTube video about Noam Chomsky’s theory of false flags, and now see conspiracies lurking under every bed. Just ask the staff of the Washington pizza restaurant where a gunman opened fire, having read some online imaginings about it being part of a child sex ring linked to Hillary Clinton. Ask Leonard Pozner, whose six-year-old son died in the Sandy Hook school shooting and who has been persistently harassed by truthers arguing that the whole thing was a hoax; that nobody died really, and that the grieving parents should stop “pretending”.

Lurking at the bottom of this pond, alongside the people convinced that MI5 murdered Princess Diana, are those suggesting that the prime minister would rather let little girls die than face tricky questions about her manifesto. The ignorance of most of those claiming to know the real “truth” in such cases is often matched only by the preening vanity: they alone can grasp what’s really going on. Wake up, sheeple! Behold your intellectual superiors, arguing that the Boston bombings were staged by actors.

Facebook Twitter Pinterest Edwin ‘Buzz’ Aldrin on the boom – sorry, moon – in 1969. Photograph: Neil Armstrong/AP/Press Association

But behind the swanking, there may well be some nervous self-soothing going on. Pozner has noted that some of those hounding him turned out to be parents themselves. Was it easier to insist the shooting never happened than to confront the unbearable thought of something similar befalling their children? Like a twisted form of religion, conspiracy theories can be a coping mechanism, a means of ducking harsh truths or imposing order on chaos. At least they provide the comforting illusion that someone is in charge.

What’s pernicious about these fantasies is that they feed off real doubts and mysteries, albeit grossly inflated and distorted until two plus two equals a million. The causes of autism were not as well understood two decades ago, and Andrew Wakefield’s junk MMR (measles, mumps and rubella) science flourished in this crack in knowledge. It’s not unreasonable to think an election fought in the shadow of a terrorist threat could help the traditional party of law and order, and the state did collude with paramilitaries in Northern Ireland; besides, the government’s emergency Cobra committee meets in secret, so can anyone outside the room really know what happened? Like mushrooms, conspiracy theories grow in the dark. But mushrooms also need manure, which is where social media comes in.

I don’t know how my friend’s grandfather devised his moon landings theory, but today he would probably have found it online. The internet’s magical power – that by expanding social circles to millions worldwide it allows the like-minded to find each other, however esoteric their interests – is also its sickness. There is no belief so repellent that it cannot find an echo somewhere online, and feel normalised.

Paedophiles are emboldened to learn just how many others secretly fantasise about sex with children, leading one another on to ever more violent obscenities. Troubled young men find a sense of belonging and purpose in jihadi forums. Racists stumble across Katie Hopkins, paid to advocate ideas that might be shunned if expressed at work. And conspiracy theorists on the left or right point each other to ever wilder imaginings. Extremes agglomerate, allowing extremists to amplify each other’s signal by sharing and liking each other’s views, until they all feel deliciously mainstream.

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The only real way forward is surely to reverse the burden of proof somehow; to create a new social norm that it’s for conspiracists to prove their nonsense, not for the reality-based community to waste time dismantling it. You don’t get to demand that a man whose six-year-old died at school should exhume the corpse, just to prove it happened. Your delusion is your problem, not his.

But it’s more likely that we will simply be mopping up the consequences for decades. Think of the research resources spent laboriously and repeatedly proving Andrew Wakefield wrong all so that parents would once again vaccinate their children. Pozner spends his days patiently scrubbing the internet of hoax theories about his son.

What lies ahead is probably years of doggedly nailing jelly to the wall, knowing you can’t reason with delusion, but that stupidity triumphs when sense says nothing. Maybe I’m just getting middle-aged. But there are weeks when all that seems an inordinately high price to pay for a convenient means of swapping gossip and cat videos.