But to many of us, idealism has been precisely the problem. There has been too much cavalier self-belief, too much succumbing to the messianic credo of "social justice". Many of my generation, not Sir David's, want less fervour and more common sense - and want fiercer material from our playwrights to puncture the complacency of those baby boomers at the top of the tree.
Gethsemane is inadvertent proof that British theatre has been caught napping by the credit crunch. If it is not to look out of touch with the debt-laden masses, it is going to have to work harder to understand how things have gone so badly wrong.
If we want a state-of-the-nation play that goes for broke, what we need, at the very least, is a leading Left-wing playwright prepared to hold a mirror up to the aspirations of his tribe: to confront the awkward fact that maybe it's not that the Left could do better that's the problem, but that the idea of "doing better" itself is freighted with inconsistencies.
UPDATE: Michael Billington responds in the Guardian:
I would concede there may be some truth in Cavendish's third point. We certainly need more plays that deal with the bread-and-butter issues of health, education and finance. It is 21 years since Caryl Churchill wrote Serious Money, which examined the impact of de-regulation on the City and all the computerised spivvery and reckless gambling that followed it. Clearly it is time for another play that analyses just how we got where we are today. But, to deduce from this that plays like Gethsemane about the corruption of Labour's soul and the compromises of office are irrelevant, strikes me as absurd.