When did conspiracy theories become such a substantial component of popular political discourse?

Is it an inevitable consequence of the internet having connected up all of the world's over thinkers - or more a case of the generation reared on The X-Files and The Matrix reaching its collective mid-life crisis? Or is it that truth really IS out there, and we're all finally on the verge of grasping it?

Brilliantly, there's a conspiracy theory about the very term "conspiracy theory": some say that the CIA slid it into the American vernacular in the 1960s, to help ensure that those pursuing hidden truths would be written off as cranks.

If that was the plan, it worked for a good while.

Even as popular culture became increasingly enamoured with shady puppet masters, duped "sheeple", and brave mavericks trying to expose the former to the latter, actual conspiracy theorists remained a specialised minority. At best they were entertaining oddballs, like the armchair philosophers of Richard Linklater's 1991 film Slacker; at worst, creepy, delusional would-be gurus, found haunting David Icke's website.

Fast forward a couple of decades, however, and the idea of widespread high-level conspiracy is no longer marginal. The notions that an identifiable "establishment" exists, that it manifests its overarching agenda via a managed "mainstream media", and that it has means of "staging" events and of silencing detractors have all become commonplace assertions.

Good, you might say. We should be regularly reminded that agendas exist, that disproportionate influence can be wielded by those with wealth, and that what's presented as unmediated truth may bear the fingerprints of vested interests. If anyone should retain doubts about those ideas, the past twenty years of public life has thrown up plenty of evidence - from the 2000 Florida presidential election recount to the case for war in Iraq to the Hillsborough inquiry - of a mismatch between smartened-up official versions and murky facts.

But if danger lurks in being too credulous, there are costs as well to the conviction that nothing is reliable, and "official" always equates with "suspect". There's being an active, sceptical observer, and then there's becoming a different kind of dupe - the kind who would always prefer to declare that an election was stolen than that one's own side lost; or to insist that a political correspondent has a nefarious agenda rather than simply a challenging take.

Lately I've seen it argued that the shady power of Hillary Clinton is such that she has been able to secure herself the Presidency by manoeuvring into position a preposterous opponent in the form of Donald Trump. (Quite why someone capable of circumventing the entire American electoral system would go through the rigmarole of elections at all, rather than just strolling straight into the Oval Office, putting her feet up on the desk and ordering a pizza, wasn't made clear.)

I've seen people throw out as if it's generally accepted the claim that "journalists are untrustworthy in general". (Yep: whoever they work for, all people who grew up wanting to express things about the world around them are mystically united by dishonesty. Like how all witches float.) I've seen a columnist subjected to sustained online harassment not simply for having a point of view that the reader disliked, but for thereby revealing herself to him as clearly the paid shill of some hooded consortium of international evildoers.

The Labour Party's most recent controversy played out in no small part as a battle between believers in secretive but utterly pervasive Jewish control over things, and believers in secretive but utterly pervasive anti-Semitism on the mainstream left. It even incorporated the idea that one might effectively be a walking conspiracy theory, by being virulently anti-Semitic whilst sincerely believing oneself not to be.

What's peculiar is that an approach to life that credits itself with not accepting simplistic narratives risks embracing the most simplistic one of all: that the story of our world is one of goodies versus baddies. The baddies, moreover, are credited with supernatural organisational capacities that render them capable not only of leaving no traces of a faked moon landing, or employing actors to pretend to be the victims of bombings, but of forcing every single one of the thousands of employees of a public broadcasting organisation to follow a particular party line without a single one of them objecting or going public.

"Conspiracy theorists are, I submit, some of the last believers in an ordered universe," philosophy professor Brian Keeley wrote in a 1999 essay titled On Conspiracy Theories. Far from scraping away at comforting delusions, the conspiracy mindset can provide a whole new one - one that denies the irrationality, impulsiveness and simple messiness that governs most human actions. The fact that, for instance, the Prime Minister gets so nervous around the Queen that he blurts out insults to whole countries. Or that the SNP might just have helped to usher in a Tory surge by failing to do the hard maths on the effect of its campaign.

Conspiracy theorising also risks encouraging apathy and cynicism, rather than motivation to change things. Why try to expand diversity of representation or equality of opportunity, if everyone who enters into "the establishment" inevitably becomes a slave to power? Why back a political movement if you think everyone who might fund it, promote it or write about it is a liar, and every institution it might come to influence is already stitched up? Why play at all, if you really believe that the house always wins? The logical conclusion of the conspiracy mindset isn't revolution: it's inaction.

There's more power in recognising that they people you might think are oppressing you are only people, than in crediting them with preternatural levels of awareness and influence. Even Philip K Dick, the writer most prescient about the modern state of self-perpetuating paranoia, recognised this. "Nobody is concealing anything," he wrote, "except the fact that he does not understand anything anymore and wishes he could go home."

Hannah McGill is a writer, critic and broadcaster based in Edinburgh. She writes for Scotland on Sunday, Sight and Sound, The Independent and The Times among other outlets. From 2006 to 2010 she was the artistic director of the Edinburgh International Film Festival.