QUIS custodiet ipsos custodes? Or, in an up-to-the-minute translation, who’s watching Watchmen? A new adaptation of Alan Moore and Dave Gibbons’ graphic novel is the latest television blockbuster.

For those who don’t know the original – which also became a big-budget film – it was one of the first comic books widely accepted as serious literature, something it did by subverting all the tropes of the superhero genre.

Not everyone seems able to accept that serious art can be made about people in capes or masks or with supernatural abilities – even though that would appear to rule out Sophocles, Homer and Shakespeare. The objections don’t apply to them, of course. But superhero films, as the directors Martin Scorsese, Francis Ford Coppola and Ken Loach recently complained, are not so much Juvenal as juvenile.

As with all debates these days, it’s become intemperate: Scorsese merely said that Marvel films, while “fun and good” in the way an amusement ride is, were not “my kind of thing”; Coppola claimed they were “despicable”; Loach, naturally, thinks that they are a “commodity” cynically made for “giant corporations to make a profit”.

Naturally, since Loach thinks that about everything, from cars to clothes to chicken nuggets; everything, that is, except his own film, which always heroically depicts the working class being shafted by the capitalist system, and is presumably produced in order to lose money, since profit is such a bad thing.

The only puzzle is how he’s managed to make around 30 versions of it and become the most successful director in the history of the Cannes Film Festival without making any money.

The truth, of course, is that you would have a better chance of a percentage return on your money on a Ken Loach picture than by sinking it into a tentpole blockbuster. It’s certainly less risky: I, Daniel Blake, about a man who dies after his benefits are stopped (Palme d’Or, Bafta), brought in $16 million at the box office alone; no one knows quite what it cost, but probably less than £2 million, and about a quarter of that was given to Loach in government grants and tax breaks.

By contrast, X-Men: Dark Phoenix cost $200 million, and is expected to lose about $100 million overall. But that’s capitalism for you, cynically pursuing profit by funding heartbreaking socialist narratives of neoliberal oppression, while throwing money down the stank to bring you Sophie Turner and Jennifer Lawrence as sexy mutants in spandex.

As it happens, I think Scorsese’s Goodfellas, Coppola’s The Conversation and Loach’s Kes are better films than Joss Whedon’s Avengers Assemble (to pick a superhero movie not only critically lauded, but the third-highest grossing film ever made). But this is not an especially controversial view. There is a tendency, in all the arts, for some work to be marked as “serious” and lesser work as “entertainment”.

High art is better than low art, but the genre division is nonsense. Those “serious” films are genre films, too: Goodfellas (and Coppola’s Godfather movies) are gangster movies, The Conversation is a paranoid conspiracy theory, like Tony Scott’s blockbuster Enemy of the State, and Kes is a coming-of-age tale. These are all forms as established, and with rules as clear, as science fiction, Western, war, horror, rom-com or superhero pictures.

“Literary” fiction, of the sort that makes the Booker prize shortlist, is as much a genre as space opera or detective fiction; indeed, it sometimes is one of those, even when it won’t admit it. Margaret Atwood used to protest furiously that she didn’t write science fiction (though she has softened her stance now that it’s big box office).

The “literary” quality of Iain Banks’ “mainstream” books is not notably different from Iain M Banks’ science fiction. The fact that William McIlvanney and Ian Rankin’s subject is crime and detection does not impede their reception as serious fiction. If Cormac McCarthy is a better writer than JT Edson, they are nonetheless both authors of Westerns. Donald E Westlake’s thrillers (which inspired several notable films, including Point Break and The Outfit) are recognisably in the same vein as The Count of Monte Cristo or works about revenge by the likes of Euripides, Webster or Shakespeare.

New forms of consuming media have led to much wider availability of every possible form of art – think of whole TV channels devoted to classic film, instant access to almost any music on streaming devices, and the digital reproduction of the entire history of Western visual art.

It’s also led to catholic tastes and surprising crossovers: Philip Glass creating symphonies from David Bowie’s rock music; modern retellings of classic novels; new visual responses to classical painting; postmodern architecture; period films with pop soundtracks (such as Coppola fille’s Marie Antoinette).

It’s rather a shame that it hasn’t led to a reduction of the snobbish tendency to cram things into genres to be elevated or deplored, when the best works of art are about breaking out of, or transcending, such categories.

If Aeschylus’s Prometheus Unbound is greater than Kenneth Branagh’s Thor (as it is), it’s not because of the subject matter: they’re both tales of gods and heroes.