Yvette Cooper wants a debate about immigration. I think she's wrong.

As Stephen Bush points out, Labour has been calling for such a debate for the past 20 years - and we've been having one, insofar as the mindless drivel that passes for political discourse can be called a debate.

And it's done Labour no good at all.

One reason for this is that the debate is largely dishonest. Rather than admit the brute fact that many people just don't like foreigners, anti-immigrationists hide behind claims that immigrants are bad for wages or public services. Except in a few pinch points, or to a small extent, such claims are false.

Yes, we can point this out in debate. But doing so does no good. When confronted with evidence against their prior views, people don't change their minds but instead double-down and become more entrenched in their error (pdf).

I suppose there is a reasonable debate to be had about whether discomfort about foreigners should be a basis for policy, or whether a loss of income and liberty is a price to pay to indulge such taste. But in a political-media system that selects for shrill hysteria over cool rationality, this is not the debate we'll get.

In fact, there's a positive reason not to want a debate about immigration. Ms Cooper is an economist and so should know that everything carries an opportunity cost. And the opportunity cost of debating immigration is high. Our time and cognitive bandwidth is limited, so time spent debating migration is time spent being silent about other questions.

From this perspective, debating immigration serves a reactionary function, as it silences debate about another question: is capitalism today best serving people's interests? Debating immigration encourages the idea that immigrants are to blame for stagnant real wages and poor public services, and deflects attention from the possibility that the causes of these lie instead in secular stagnation.

What Labour should be doing therefore is demanding - and instigating - a debate about how best to increase growth, wages and living standards. We should be asking not what to do about immigration but what to do about capitalist stagnation?

Such a debate would require us to call into question the viability of conventional top-down managerialist capitalism (pdf). Given limited cognitive bandwidth, this would deflect blame for economic failure from immigrants and help focus it elsewhere.

If you think I'm being pettily economistic in wanting a focus on pocket-book issues, you're massively wrong. We're re-learning today what we should have learned in the 30s and again in the 70s - that economic stagnation breeds reaction and intolerance. If you want a liberal society, you need economic growth; technocratic talk about the benefit of immigration is true, but not enough to change minds.

In fact, such a debate would serve another useful purpose. A debate about immigration brings out not just the worst in people, but the worst of people: it legitimates the reactionary drivel of Farage and Hopkins, and encourages the media to give them publicity. Shifting the debate to growth would filter out such noxious fumes: the likes of Farage have nothing worth saying about economic stagnation. Yes, it would mean hearing more from the IEA and the We've selectively read Wealth of Nations and ignored the Theory of Moral Sentiments Institute. But if these displace racist drivel, it's a big improvement.

The point I'm making here is one made by Steven Lukes. Power consists, in part, in shaping the agenda - in deciding what gets debated and what doesn't. Insofar as debating immigration means not debating the health of capitalism, it plays into the hands of the powerful.