How can I put this? Wee Jimmy Krankie in yellowface is not the hill I want to die on. But let’s rewind: on Monday the American comedian Margaret Cho tweeted a magnificent denunciation of the news that Janette Tough, the Scottish schoolboy-impersonator, is to appear in the new Absolutely Fabulous film as a Japanese fashion designer called Huki Muki. Obviously, this sounds appalling. As someone whose childhood was blighted by the Krankies, the news that their creator is still working – when fine thespians such as Russ Abbot and the Chuckle Brothers are consistently passed over by the academy – is a travesty.

But that’s not what got Margaret Cho’s goat. “I AM FUCKING SICK OF YELLOWFACE,” she tweeted. “Have some respect. Hire Asian actors 4 Asian roles. I’m not going to name the production but I’m DISGUSTED!” In her next tweet, she named the production.

Cho’s comments were particularly interesting because she has been accused of “yellowface” herself. In January this year, she appeared alongside Tina Fey and Amy Poehler at the Golden Globes, dressed as a North Korean general, in a bit that referenced the Sony hacking scandal. But neither that, nor the fact that Cho’s family is Korean, was enough to protect her. The routine was a “gross and unfunny bit of yellowface minstrelsy” wrote Richard Kim at The Nation.Vulture called it an “empty caricature” that played to a majority-white crowd’s “racialised expectations”. Cho’s defence was simple: “I am from this tribe. And so I’m able to comment on it.”

This argument – about who gets to impersonate whom – keeps coming up, and rightly so. Power in Hollywood largely rests with white men, and their dominant gaze is reflected in the films we consume and the lessons we take from them. More diverse stories and more diverse casting are a straightforward social good. Films should show that women can be the protagonists in their own lives,; that two men can have a love affair as intense as any straight couple’s; and that black people are not the world’s supporting cast.

But sometimes I feel as though everyone except me has access to a rule book on this stuff. For example, I’m prepared to concede that Janette Tough playing a Japanese man might well be crude, unfunny and reliant on stereotypes, treating racial difference as a punchline (although I’d prefer to see the film before making that claim). OK, then. But isn’t her portrayal of Wee Jimmy Krankie similarly offensive? You can muster a pretty good argument that Scottish schoolboys are victims of historical oppression: they have lower life expectancy than their English counterparts, and poor white children do worse at school than any other ethnic group. What? No takers for that? Oh, OK.

Then again, we’ve always had a cross-dressing exemption in these arguments about the offensiveness of impersonating a marginalised group. After all, at this time of year the country’s hippodromes are full of middle-aged men parodying the stereotypical failings of women – silly, bawdy nags – by playing pantomime dames. The Ab Fab movie is rumoured to feature up to 100 drag queens performing a caricature of femininity. Yet it’s only when the target of the mockery is updated from boring old women to non-binary people – as with Benedict Cumberbatch’s androgynous supermodel in the Zoolander sequel – that an internet storm ensues.

As someone who considers drag to be ultimately playful and liberating, I do believe that there is a meaningful difference between it and yellowface. But it’s a difference that needs unpicking, and at the moment I feel like a year seven maths teacher: it would be really helpful if people showed their workings.

And there are other rules I’d like to propose. First, it would be great if everyone involved could see the film first, rather than rely on two-minute trailers. (Robert Downey Jr’s blackface in Tropic Thunder is not the same as Anthony Hopkins’s in Othello.) Second, attack the system, not individuals. Casting isn’t purely in the gift of the writer or director, but is often imposed by studios. (One of the saddest quotes in existence is Lee Child talking about Tom Cruise portraying his 6ft 5in hero, Jack Reacher, on screen. “Reacher’s size in the books is a metaphor for an unstoppable force,” said Child. “Which Cruise portrays in his own way.” His own adorably tiny way.)

Next, make sure that the demand for minority actors to play minority roles doesn’t transmute into the idea they can play only minority roles. Rupert Everett has said that coming out as gay led to him being typecast: goodbye, leading man; hello, sarcastic best friend.

Tom Hollander says a similar thing happened to him when casting directors simply assumed he was gay after he played several gay roles. “I could probably have paid for half of a quite modest central London one-bedroom flat on the proceeds of my work as a homosexual impersonator,” he writes in the latest Spectator. Still, there was a silver lining: “I like to consider myself a blank cheque on which people are free to ascribe whatever value they feel appropriate.” Perhaps the woman behind Wee Jimmy Krankie feels the same.