Talk that Miliband is considering breaking Labour's link with the unions poses the question: why should reasonable people think distancing itself from the unions can win the party votes?

Let me first deepen the puzzle. Nobody under the age of 40 can remember when unions were (plausibly or not) accused of wrecking the economy. Indeed, these days, the wreckers are not unions but managers. From bankers causing recession through bosses plundering their companies to BBC executives stealing licence-payers money, the economic vandals today are bosses, not unions.

What's more, it would be easy to argue that stronger unions would be in everyone's interest, and not just because they help restrain managerial parasitism. They represent the "little platoons" that Tories should admire, and could be part of the "big society" that allows state regulation to be scaled back. And it's quite possible that the higher wages unions want would help the economic recovery by increasing aggregate demand.

Why, then, are unions still seen as the big bogey man that Labour feels it must distance itself from?

Obviously, Tories and capitalists and their lackeys in the media want to divide and rule their opponents. But why does Labour give credence to their demands? I suggest four reasons.

1. Path dependency. Because we are all slow to change our minds, beliefs can persist after they've lost their truth and utility. The idea that unions are greedy wreckers thus persists long after it was possibly true - just as the idea that Tories are racist persists.

2. Modernity. Unions are seen as relics, dinosaurs. But a big part of Labour's managerialist ideology is the desire to present itself as "modern." Miliband is thus wary of associating with the unions for the same reason he doesn't wear kipper ties and Noddy Holder sideburns.

3. Individualism. The spirit of our age is the antithesis of the spirit of '45. People think they can advance themselves by individual, not collective effort. The ideology that gave us the 1945 government was created by the War. Today's ideology is created by the X Factor and Apprentice, and the pursuit of "winner take all" prizes rather than ensuring an adequate reward for a decent job.

4. Presentation. Unions are lousy at hegemonic strategies. The rhetoric of "fighting" and "demands" makes them seem a tiresome sectional interest rather than a group whose interests are the national interest. And of course the media - including the ever-neutral BBC - reinforces this. Whereas bosses are often invited to give a "neutral" and "expert" opinion on the economy, working people rarely are. "What's good for GM is good for America" was long a plausible slogan. The slogan "What's good for Unite is good for Britain" has never even been tried. Perhaps, therefore, unions themselves are partly to blame for their political marginalization.