• Editor's note: there are Season 3 finale spoilers in this piece.

In one of the more famous moments in the Showtime thriller, Homeland, Saul Berenson – a man who looks like he should be teaching ethnomusicology to doe-eyed liberal arts undergrads, but instead is the acting director of the CIA – tells his impetuous, deeply unstable and yet oddly prized analyst Carrie Mathison that she is "the smartest and the dumbest fucking person I've ever known".

Smart and dumb are excellent descriptions for Homeland, which in its scintillating first season conflated absorbing character studies with plot points so utterly implausible that it left viewers not sure whether to hate the show or love it.

The initial impulse of many, at least initially, was the latter. Here was a taut, well-acted story with a deeper thematic message about the blowback effect of America's post-9/11 obsession with terrorism. Carrie, along with the show's other tent-pole character, Marine Captain (turnedal-Qaida terrorist) Nicholas Brody, offered a sobering tale of how the dogged pursuit of a global war on terrorism can do great harm to both those targeted by it, and those tasked with fighting it.

So what if portraying the CIA as a paramilitary organization, operating practically at will in the United States, was absurd and so clearly illegal that it was laughable; so what if the lead analyst in the show not only regularly broke the law but had a mental illness so severe she wouldn't have made it through five minutes of a CIA-mandated polygraph; so what if many of the show's characters, from the cartoonishly malevolent vice president to Brody's children appeared to have emerged fully-formed out of Hollywood's "Big Book of Sullen and One Dimensional Stock Characters"? The show was a true Sunday night guilty pleasure.

But after two seasons of some of the "dumbest fucking" plot twists in recent television history, it's hard to imagine that many are still capable of watching this show with a straight face.

Suspension of disbelief is one thing, but Homeland has gone far beyond that. This season alone, the producers of Homeland offered four episodes of Carrie's further descent into madness and betrayal by the CIA … and then basically said: "Psych! We were just kidding; ignore everything you've seen." But this bit of subterfuge was all in pursuit of a larger goal: Saul's plan to bring the No 2 official in Iran's Revolutionary Guard, Majid Javadi, to the United States (mind you, this is the guy who is the alleged mastermind of a car bomb attack against the CIA that ended season two) and turn him into a double agent working against the Iranian government.

Meanwhile, when Javadi savagely kills two people (including his ex-wife) Saul stops a police investigation into the murder … and does all this, by the way, without telling anyone else, including the White House. And of course no one finds out because, after all, if there is one thing we know about the US government – especially here at the Guardian – they do a bang-up job of keeping a secret.

Meanwhile, Saul brings Brody (who is, by the way, the most wanted man in the world for that bombing) back from the daze of heroin addiction in Caracas (don't ask) to sneak across the border into Iran and kill Javadi's boss, so that Javadi gets the top job … and then peace breaks out, or something.

In between all this, Carrie gets shot by her fellow CIA agent for disobeying an order and trying to prevent the murder of a suspect in the Langley bombing who gets murdered anyway – and yet no one seems to care. Yet not only is she in perfect health a week later, but Saul decides she is the best possible person to go undercover to Tehran and assist in getting Brody out of the country. Oh, did I mention that she'spregnant with Brody's baby?

Like I said, fucking stupid.

But as ludicrous as the plot developments have been this season, Homeland's real crime is that it's peddling a dangerous set of lies about terrorism, American omnipotence and the very nature of international politics.

When Homeland first appeared it did something culturally unique. It provided viewers with a perspective rarely seen in the decade since 9/11 – that of the suicide bomber. Nicholas Brody didn't hate America because of its freedoms; he hated the nation that sent an unmanned drone to northern Iraq and killed the young son of the terrorist mastermind (Abu Nizar) who was holding him a prisoner. This season, Homeland eschewed such nuance, instead portraying al-Qaida and the Iranian government as being in actual cahoots – even though there is no love loss at all between these two Sunni-Shia rivals. Iran and its people are presented as a caricature of anti-American hatred – one that looks nothing like reality.

In addition, Homeland never bothered itself with the niceties of global diplomacy. It is a show that presents change – or the potential for it – as being most likely found at the end of a gun barrel. This season it doubled down.

In its make-believe world peace and rapprochement between long-time enemies is achieved not through the extension of an olive branch or even the application of political pressure, but rather a CIA assassination, which somehow melts away years of animosity between the US and Iran and transforms the Middle East.

This is a bit how children understand foreign policy – grand sweeping gestures crafted by well-meaning individuals (or in this case a psychopathic killer being blackmailed by the CIA) that somehow transform whole societies. Indeed, when Saul unveils this grand plan for peace to Carrie, he tells her that, if successful, "two countries who haven't communicated for 30 years, except through terrorist actions and threats, can sit down and talk." But, of course, for that to happen, someone has to die first.

The irony of all this fictional intrigue is that at practically the exact moment that Saul uttered these words, two countries that hadn't communicated for 30 years were sitting down and talking in Geneva – and reaching an agreement on limiting Iran's nuclear program.

Indeed, if there is anything we've learned about international relations this year, it's that the way countries often find agreement is through a series of very un-sexy activities: plodding diplomacy, laboriously constructed sanctions regimes, confidence-building measures and protracted negotiations. And even then there is hardly guarantee of success.

The recent breakthrough in Geneva between the US and Iran was not a result of CIA manipulation or American skullduggery, but rather the strategic decision-making of leaders in the United States and Iran (as well as France, the United Kingdom, China, Russia and Germany) to pursue normalization. Of course, on Homeland, the Magical Mystery Tour season ends with Saul Berenson being given sole credit for transforming the strategic calculus of the Iranian government – and the achievement of a nuclear deal in Geneva.

A show that labored (often successfully) in its first two seasons to offer nuance in its depiction of jihadist terrorists – and a sordid glimpse into the unintended consequences of American militarism – has become a paean to the supposed strategic brilliance of the CIA, the tactical efficacy of US special military operations and a dispiriting, black-and-white portrait of America's "Muslim" enemies.

Making bad television is sin enough, but Homeland does far worse: it not only misunderstands the Middle East, it fetishizes the worst elements of American power and misrepresents how and why international political change occurs.