You can see his point. But for an unsympathetic character, Medea has proved surprisingly popular. When Kent's production of Euripides' tragedy opened at the Almeida Theatre in 1992, one critic reckoned it was the seventh to hit London in 10 years. Diana Rigg's success in that production, transferring to Broadway and the West End and transforming her status as a classical actress, only served to confirm that Medea has become the great peak of the classical repertoire for women. But it isn't only in Euripides' version that Medea survives: the story has inspired countless more or less faithful retellings, from Pier Paolo Pasolini's carefully literal-minded film version, set in a mythological landscape with real centaurs, to Toni Morrison's 1987 novel, Beloved, which echoes the myth in its story of a slave who kills her child to keep her from slavery.
In particular, Medea's boundless, raging passion has made her a favourite heroine of opera - the Oxford Dictionary of Opera lists no less than two dozen works on the theme, from Cavalli's Giasone in 1649 through to Gavin Bryars' Medea in 1984. The version most celebrated in our own time has undoubtedly been the Cherubini of 1797, if only because it was one of the roles with which Maria Callas became identified (completely enough for Pasolini to cast her, against the grain of his usual unstarry practice, in his 1970 film). Cherubini's Medee hasn't been seen on stage very often in this country, even though Callas's advocacy was enough to turn it into one of the peaks of the operatic repertoire, just as the Euripides version is a peak of the theatre. Phyllida Lloyd, director of the Opera North production which opens tonight in Leeds, describes the third act, in which Medea holds the stage virtually uninterrupted, as an "Anapurna" (the first singer to attempt the part is supposed to have died from consumption brought about by the extreme demands it placed on her voice). You hope Josephine Barstow will come out of the ordeal relatively unscathed.
Why has Medea endured so well? One answer is that it is a woman's play. Jonathan Kent says that rehearsing his production was often an unnerving experience - the play is dominated by Medea herself and by a chorus of women, so that much of the time he found himself the only man in a woman's world. And Medea is a uniquely strong woman in classical tragedy - even Electra, it's been remarked, could only urge a man to do the killing; Medea makes it all her own work.
Before Euripides - and in some later versions - Medea was a supporting character in what was fundamentally Jason's story. She helped him to steal the Golden Fleece from her father, the king of far-off Colchis, along the way murdering her own brother and duping Jason's nieces into doing away with their father. Euripides starts the action some years later in Corinth, where Jason has thrown Medea over and is planning a more advantageous alliance with the daughter of Creon, the local king. Worried - quite rightly, as it turns out - by how Medea might take this, Creon banishes her and the two sons she has had by Jason; she reacts by sending her rival a poisoned tiara and gown, which see off both the princess and her father, and then completes her revenge on Jason by putting their sons to death. She is last seen hovering above the stage in a chariot drawn by dragons, enjoying a gloat over Jason's misery.
It's by no means a pretty tale; but what's remarkable is, as Kent points out, how sympathetic a character Medea is. That's largely because Euripides reverses traditional notions of manly and womanly virtues. At one point, the chorus of Corinthian women, who for most of the play offer Medea their sympathy and support, lament that (in the words of Philip Vellacott's Penguin Classics translation): "Streams of the sacred rivers flow uphill/ Tradition, order, all things are reversed/ Deceit is men's device now/ Men's oaths are gods' dishonour." Jason is a far-from-heroic figure, his self-justifications pathetically feeble in the face of Medea's hatred. Phyllida Lloyd, who has the distinction of having directed both the Cherubini and the Euripides (at the Royal Exchange in Manchester, in 1991), recalls being "reduced to helpless laughter by some of the lines Jason tries to spin her - you know, `This is a really good move for all of us, that I'm going to take a younger wife, try to see the positive side of it.' "
But while there's a case to be made for the Euripides as a proto-feminist text, that can't by itself explain the persistence of the myth. Other versions of the story, the Cherubini among them, have made Jason far more a square-jawed, clean-cut hero, Medea far more a Wicked Witch of the East figure, who ends up being burned alive as punishment instead of flying off with her dragons. These are the versions that Tony Harrison attacked in his brashly titled Medea: A Sex-War Opera, in which we're informed, "Medea is a murderess in the history/ Of men who plotted against the great she..." - that opera ends with a plea for the kind of understanding that Euripides showed.
The fact is, though, however black she's painted, Medea still exerts a fatal attraction. Phyllida Lloyd admits to being somewhat disappointed when she first came to Cherubini to find that Jason was "comparatively the nice guy", as opposed to the "pragmatic bastard" of the Greek: "When I first heard the music, the classicism of it, the order of it seemed an absolutely bizarre texture in which to express anything to do with Medea. I found it far too formal, anal, lacking all the chaos, all the dissonance that I'd associated with the myth, and that had come to me through the Euripides."
Working on the opera, she has come to appreciate that this classicism creates a context in which you can express what is "in some ways... a clash between nature and civilisation". Within that setting, Medea's vocal gymnastics point to her otherness - not only is she a woman in a man's world, she is also, coming from Colchis, a barbarian. This aspect of the story is made most obviously in Pasolini's version - "anthropological cinema", he called it - which depicts Medea as a high priestess in a society bound up with ritual and the rhythms of nature, opposed to the superficial rationality of the Greek world.
This sense that in Medea we're seeing emotion let loose and rationality and pragmatism overwhelmed is, maybe, the real source of the myth's power. In the awful destructiveness of Medea's revenge, what we're seeing is the feebleness of reason in the face of feelings. Perhaps that's what makes it so horrifying; or perhaps, seeing what rational horrors have been committed in this century, that makes it optimistic.
Opera North present `Medea' at the Leeds Grand Theatre tonight, 7.15pm. To 26 April. Booking: 0113-243 9999