In search of the new Noël Coward? You should probably give a wide berth to the Twitter mentions of critics sceptical about Avengers: Endgame. “Eat dirt and die, trash!” is typical feedback. Likewise: “I hope Stan Lee haunts you, slut” and “Fuck you, bro, fuck you”. Fanboy ire is not new. But its power – both in the moment and over the longer term – is on the rise. Not that Avengers: Endgame is necessarily the best example, of course. The final instalment in a 22-film cycle has earned almost universal five-star reviews, including in this paper.

Tony Stark’s climactic battle with Thanos and his Infinity Stones may well be up there with the best of Kubrick, Hitchcock and Kurosawa. If a professional believes this to be the case, it is their job to tell us. The certainty of being slagged off on social media as being bitter, angry, moronic, whiny, bitchy, brain-damaged, drug-addled, outstandingly incompetent and unloved by your mother should you suggest otherwise would not sway most of those critics I have come across.

Yet, for a few, it might just make the difference. What was once the job of publicity departments – to prod the paranoia of people with a dread of seeming out-of-touch – is now carried out gratis by eager millions desperate to defend vulnerable underdogs such as, er, Disney.

“Let me tell you eggheads,” a man called Max told a Canadian reviewer ambivalent about the new Avengers. “If something is better than all your filthy criticism, you better retire and kiss the feet of the @Russo_Brothers [the directors] that his job was bigger than your whole life in that environment bastard!” You can’t blame the studios for leveraging such passion. Marketing a movie as a “love letter to the fans” gives the whip hand to the audience. If you don’t like it, you’re the one who’s lacking – you’re either not enough of an aficionado, or a really ungrateful one.

Added layers of critical immunity come courtesy of Disney’s co-option of a once-thorny conversation about diversity. Think you were risking wrath by questioning the quality of Avengers: Endgame? Just try bashing Black Panther.

Scarlett Johansson plays Natasha Romanoff in Avengers: Endgame. Photograph: Allstar/MARVEL STUDIOS/DISNEY

We are all capable of grade inflation in the cause of cowardice. No one wants to admit wasting £80 and three hours to see a rubbish play, so we moderate our reaction when the curtain falls. Editors like me welcome upbeat articles as a happy contrast to the news, and to justify the space. Why bother running cinema coverage at all, if the big films are nothing to write home about?

The cumulative effect of compulsory positivity, however, is guaranteed disappointment. The tyranny of niceness discourages anything that might immediately upset anyone. Celebrities are particular beneficiaries of this phenomenon, as people see them as friends who should be protected – often, it seems, from impoverished freelancers. And the emergence of protected categories creates no-go areas for criticism: witness the steep decline in one-star reviews that amusingly trash a movie. It’s currently almost impossible to poke fun at any but a very select group of targets.

Allied to this is a growing thirst for affiliation on the grounds of identity, which has enabled the fan clubs of old to snowball into impassioned tribes. Religion may be in decline in the western world, but cultish behaviour – hello, Max! – is evidently going strong.

Cultural commentators aren’t influenced only by their readers and editors, but by everyone else too. Their fondness for acclamatory orgies, and for rating according to political criteria, is part of the trahison des clercs prompting a wider retreat from truth and reason. We now bow down before emotional indulgence rather than analytical thought. And elites scrambling to protect their hegemony lower their heads too, even if they’re secretly crossing their fingers.

Implicit in this new cultural environment is a rejection of expertise. If we subscribe to the idea that there’s no such thing as an objective standard of quality in art, that there can be only subjective opinions, then anyone’s take is as good as anyone else’s: “what I think is good” blurs into “what I like”. Criticism teeters on the brink of pointless personal response.

In such a world, congratulation flatters everyone. “I like stuff lots because I’m big-hearted and have a bottomless ability to appreciate” also means: “You’ll really like this because you’re similarly wonderful.”

Earlier this week, the Irish Times critic Donald Clarke gave Avengers: Endgame three stars out of five. The verdict on Twitter? This man “simply hates fun”. Perhaps this is true; I’ve not met him. But to paraphrase the bookies: when the fun stops, stop pretending it hasn’t.

• Catherine Shoard is the Guardian’s film editor