A cabal of politicians and celebrities engaged in unspeakable acts. A saviour battling to deliver the world from evil. And an enigmatic whistleblowerSomeone who exposes secretive behaviour by a group or organisation; once used to describe police who blew whistles to signal the scene of a crime. feeding morsels of truth to the brave few, wise enough to listen.

This may sound like the set-up for a schlocky sci-fi series. But QAnon - a conspiracy theoryAn explanation for a phenomenon that centres around the actions of sinister, shadowy groups, where an absence of evidence can be interpreted as evidence of its truth. claiming that US President Donald Trump is destined to destroy a shadowy network of SatanistsPeople who worship the Devil of Judeo-Christian religion. From the Middle Ages onwards, there have been countless examples of people and groups persecuted for alleged Satanism. - has attracted hundreds of thousands of devotees.

One recent poll found that 56% of Republicans think QAnon is at least "partly truthful". On Tuesday, Facebook announced that it will actively remove all pages, groups and Instagram accounts linked to it.

QAnon was spawned in 2017, after an account named "Q" began spreading cryptic messages on 4chanA website on which users can anonymously post images and messages, and the subject of several controversies.. It was quickly disseminated through social media, gradually seeping out from the US to spread across the world.

Along the way, it has absorbed several other conspiracies, including the notion that the Covid-19 pandemic was planned by Trump's enemies.

For many, the purge of QAnon cannot come soon enough. Indeed, some argue that all conspiracy theories should be totally banned. After all, many countries have legislation against defamationA false claim that harms an individual's reputation; if found false in court, the victim can be awarded damages. In 2017, a jury in New Hampshire awarded three businessmen a record 4m.. The spread of dangerous misinformation, often containing false allegations against individuals, should be subject to similar penalties.

Historians point out that conspiracies fuel prejudice and encourage discrimination. In the 1950s, the Red ScareA conspiracy claiming that covert communists were plotting to take over the US. gave rise to McCarthyismA series of vindictive investigations, led by US Senator Joseph McCarthy against suspected communist sympathisers, including high-profile celebrities like Charlie Chaplin and Orson Welles. Many victims were blacklisted from working or even imprisoned.. The FBI has named QAnon a domestic terrorist threat following numerous cases of attempted violence, including a threat to assassinate presidential candidate Joe Biden.

Governments censor media that incites criminality and hatred; they should ban theories that do the same - so the argument goes.

Others, however, insist that conspiracies and their theories should be left alone. QAnon might be wildly implausible. Yet some far-fetched tales have turned out to be correct. The CIA's MK-Ultra programme to control minds using hallucinogenic drugs, for instance, was a conspiracy theory for many years before it was revealed to be true.

To impose a blanket ban on theories could smother some uncomfortable truths.

Many believe it would also curtail our freedom of conscienceThe right to hold our own viewpoints independent of those of others.. To prohibit conspiracy theories is to police what people can and cannot think. If theories are banned, where does one draw the line? We are then well on the way to authoritarianismA form of government in which individual freedoms are severely limited by government power. Examples include Nazi Germany, Khmer Rogue Cambodia and contemporary China.. We should ensure that lies are promptly identified, but trust people to judge their validity by themselves.

Stop the hubbub, say some. Conspiracy theories have a proven history of damaging lives, livelihoods and liberty. The likes of QAnon pervert people's perception of the world, revive deep-seated prejudices and even encourage violence. We should lance such boils.

"Never!" counter others. Start banning theories and you start banning thought itself. Though we might personally disagree with a conspiracy theory, we should respect the choice of others to believe it.