'Break a leg" is a phrase one frequently hears outside theatres and opera houses. Usually, of course, it means "good luck". At the moment though, it's just as likely to be meant literally, as a piece of advice for singers on how to deal with opera critics.

At the heart of the storm enveloping my profession are the remarks made in five broadsheet reviews of Glyndebourne's new production of Strauss's Der Rosenkavalier. In a rare example of unanimity each review, including this newspaper's, pointed to a problem with the portrayal of the work's hero, Octavian, who was described variously as "stocky", "dumpy" – and in the case of the Financial Times, "a chubby bundle of puppy fat". Octavian, a male character but written for a female voice and thus always played on stage by a woman, is a tricky role for a number of reasons, not least of which is that a married princess, a young bride-to-be and her country squire fiance are all supposed to find him devilishly attractive, either when he is dressed as himself – a 17-year-old playboy aristocrat – or as a chamber maid called Mariandel. Oh yes, and the actor playing this improbable Adonis has to be able to sing like a goddess.

In the case of Glyndebourne's new staging, the director Richard Jones sought to make Octavian look more a gauche teenager than a self-assured aristocrat. Tara Erraught, the mezzo-soprano cast in the role, was given a Little Lord Fauntleroy-style, curly wig, a suit too tight in several places, and "bum-fluff" stubble on her chin. Her Octavian runs against what we assume to be true about the character, and in so doing disrupts our understanding of why, in each case, the three other characters want so desperately to get into her, sorry I mean his, trousers.

I'm not here to defend the choice of words some of my colleagues used, but no one seeing the performance could reasonably fail to comment on Octavian's appearance. Indeed, any reviewer not asking questions about this precise point would be failing in their duty to hold the production and its performance to account. None of the reviewers involved dispensed gratuitous misogyny. But this is what, in numerous newspaper articles and columns, radio programmes, and in thousands of tweets and Facebook posts, they stand accused of. Which is ridiculous.

Opera critics, writing in the daily press, usually have between 300 and 500 words to review a production, so there's quite a bit of shorthand involved. And part of that shorthand is a conflated way of talking about stage characters and singers in a single breath.

But even given more space, the problem would remain. In opera, characters and singers are harder to keep apart than in classical theatre. That is because opera is also, or even mostly, about singing. And while when looking at opera we may be furnished with an illusion of stage characters inhabiting dramatic roles, we also experience in a more direct way the particular voices of singers who, while acting with their bodies, are singing in their own voices.

This bleeding of the personal into the abstract, and the blurred lines between theatrical illusion and enhanced physical presence through unamplified voices, may well constitute an argument about why opera critics should be more circumspect than others in their remarks about singer's appearance.

But it is also one of the reasons why opera is an art form capable of generating levels of passion, and beauty, which are unique among the arts. Indeed, given the form's uniquely high production values, and the opportunity for finding life-enhancing beauty in every little physical and conceptual detail arrayed both on the stage and below it in the orchestra pit, we should be straining every sinew in trying to defend it, and its proper criticism.