A leaflet from the Lib Dems sullies my doormat decrying "heartless Tories" and "clueless Labour", echoing Clegg's claim that the Lib Dems would "add a heart to a Conservative government and add a brain to a Labour one". This seems to me to be doubly wrong.

I don't believe the Tories are especially heartless. I suspect Michael Gove was sincere in wanting to improve the education of the worst off, and I even suspect Iain Duncan Smith really does want to reduce poverty; he's just gone about doing so cackhandedly.

In fact, in many ways, the Tories have been brainless: imposing a costly and unnecessary austerity; shambolic welfare reform;a non-existent foreign policy; and a daft promise to cap immigration, to name but a few.

Equally, though, the implication that the left is all heart is also dubious. Labour's demand for immigration controls is a heartless attack upon the poor. And I suspect that many leftists use identity politics as cover for brute careerism.

Hearts and brains are bi-partisan; they are spread across the political spectrum - as is their absence.

However, the Lib Dems aren't proposing this false dichotomy merely because they are a party without principle who can only define themselves by what they are not. The "cruel right" and "silly left" are old prejudices. In 1988 Alan Blinder wrote a book Hard Heads, Soft Hearts in which he tried to combat that distinction. And in 1996 Tony Blair complained of the longstanding but "foolish" tendency to regard Tories as "cruel but efficient" and Labour as "caring but incompetent."

I suspect these prejudices reflect two errors.

One is a form of naive cynicism which regards inequality and injustice as natural and inevitable, and so attempts to fight it must be futile and foolish whilst defenders of the system are hard-headed realists.

The other is a tendency to underweight the incompetence of those who are on the side of the rich.

Hostile portrayals of capitalists have for decades been of Gradgrindian figures grinding the faces of the poor rather than of bumbling oafs. And today bankers are routinely described as greedy when in fact what distinguishes them from the rest of us is their stupidity: most of us like a pound, but we didn't destroy an entire industry.

What this misses is the likelihood that a lot of success in business might be due to dumb luck.

In this sense, the claim that the the rich are heartless, by understating their stupidity, actually helps to legitimate inequality.