David Cameron says the role of government should be to help film-makers 'to make commercially successful pictures.'

Leaving aside the question of whether governments should be involved in the film industry at all, this runs into a problem - that it is impossible to predict what films will be commercially successful. The best brains in Hollywood devote themselves to this question, and they cannot succeed - which is why they so often rely upon sequels, boring proven formulae and multi-million salary stars.

So obvious is this point that it has led to the strange sight of right libertarians supporting Ken Loach.

However, when an intelligent man says something so silly, something must be at work. That something is ideology. What we see in Cameron's remark is an extreme manifestation of managerialism - a belief that something unpredictable (the public's film tastes) can in fact be foreseen in advance by experts in government.

This sort of hubristic failure to acknowledge unpredictability could only exist in people who have no knowledge of actual management or business. As Hopi says, the political class are people with almost no credentials who think that 'changing Capitalism requires only a couple of press releases, a press conference, and a pamphlet from a friendly think tank.'

But herein lies something odd. We've seen in the last few days media outrage about tweets by Diane Abbott and Ed Miliband; 'Blackbusters' - the term they use in Uruguay, I gather - made the front page of the Sun. But these were casual, off-the-cuff remarks. Why, then, has the media made so much less fuss about an equally stupid remark which was made after some thought, and which has genuine policy consequences?

It could be because we have a dumbed-down Tory-biased media that obsesses only about trivia.

It could be because those tweets play to the prejudices that Ms Abbott is a racist firebrand and that Mr Miliband is just hapless - and the function of the press is to reinforce prejudice.

But maybe something else might be happening. The media share the ideology of the political class, and also believes in the fiction of a predictable and manageable world. It is therefore incapable of seeing the absurdity of Cameron's remark.

In this sense, managerialism is a truly powerful ideology, as its blinds its possessors to the fact that it is (to say the least) a partial and contestable view of the world.