(Note: this article is spoiler-free)

Survey the footage trailing Troy: Fall of a City – bearded men in togas, battles on horseback, the kind of candlelit sex scenes that will make watching episodes on public transport particularly tricky – and you'd be forgiven for thinking it was business as usual. Another blockbuster (albeit a small-screen one) depicting Homer's mythical tale of war, gods and doomed love.

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But BBC One's splashy new eight-parter created by The Night Manager's David Farr approaches this ancient story with something of a modern sensibility. And so it is that the character of Achilles, last embodied on screen by a lank-haired Brad Pitt in 2004's Troy, will this time be played by British-Ghanaian actor David Gyasi. (Not to mention many other black roles in the series, including Hakeem Kae-Kazim as the god Zeus.) It's a casting move that – with thudding, tedious predictability – has been met with opposition by a small, stubbornly vocal section of the internet.

"Homer in the Iliad repeatedly describes Achilles as 'blonde' and 'golden-haired'," whined one definite non-racist. "Mad PC decision," tweeted another. "Would anyone be mad if I made movie [sic] about US history, and actor playing Obama would be white?" chipped in one more.

"#Netflix so you're going to black wash troy fall of city the new show. zeus, achilles wasn't black and more. as a Greek I am disgusted," said one, in the interests of asserting Greek identity more than diminishing black actors, of course.

Cue an enormous sigh. Of course, there's a temptation to just ignore these micro-furores (see also: the failed Reddit campaign against Black Panther and the infamous, unavoidably hilarious 'De-Feminised Cut' of The Last Jedi) and not even give them the oxygen of publicity.

But, equally, as pop culture strives (however slowly) to make itself more ethnically representative, it's important to remind ourselves exactly why these tiresome, faux-concerned responses are so gloriously wrongheaded. So let's break it down. Firstly, there's the question of Homer's intentions upon crafting this martial epic at least 2,700 years ago.

BBC

Putting aside the fact that, in a mythical world of vengeful deities flinging thunderbolts and armies hidden within giant wooden horses, you'd hope that audiences would be able to somehow accept – gasp! – a superhuman warrior who isn't a white dude, there seems to be a selectiveness to this supposed desire to cleave to Homer's authorial specifications.

Yes, one passage of The Iliad refers to Achilles' fair hair, but there's also the suggestion that he was over 10 feet tall. So why no online campaign to have him played by The Mountain from Game Of Thrones or Andy Serkis in a mo-cap suit?

Then there's the notion that it's simply Gyasi's obvious lack of Greek heritage, not his race, that's an issue. Again, even if we conveniently ignore the fact Australian actor Louis Hunter is playing Paris (the Trojan, i.e. Turkish, prince), this is basically nonsense.

BBC

Is it impossible to conceive of a black Greek man? What if he was mixed race, would that be acceptable? Would he seem more plausibly Greek? It's a reminder that these arguments can't withstand even the tiniest scrutiny. What those who object to Gyasi's casting are really saying – beyond the handwringing about cultural authenticity – is, essentially, that they want to go back to the old days when you could get away with an all-white cast. When a grand, period saga like this would be a stealthy way to lock out non-white actors.

Ultimately, Gyasi – a commanding performer with impressive turns in the likes of Interstellar on his CV – is more than qualified for the part of Achilles. And it should be noted that the theatre, where Farr made his name, has been casting performers of all races in supposedly white classical roles for a long, long time. In fact, this world (of black Hamlets, Macbeths and Henry Vs) may point to where film and television is steadily heading.

And this inclusive new landscape – with its black Stormtroopers and mixed-race Asgardian heroines – is bound to cause some friction, some reckoning with our own deeply held preconceptions.

But it makes sense to truly consider why a surprising casting decision, whatever it is, makes you bridle. If you're unsettled – if the status quo of a bottle-bleached Brad Pitt is challenged by a brooding, intense Londoner bringing something completely different to a role – I'd humbly suggest that that is a very good thing indeed.

Troy: Fall of a City begins tonight at 9.10pm on BBC One.

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