Sarah Mulley has written an intelligent and reasonable piece on immigration. And this is my problem; this is an issue on which intelligent people should not be reasonable.

She says that "immigration is important for growth" and that the coalition's cap on immigration "appears to make no economic sense". She's right. Jonathan Wadsworth's brief survey (pdf) says there's "little evidence of overall adverse effects of immigration on wages and employment for people born in the UK." A new study by Francine Blau and Lawrence Kahn says "most research does not find quantitatively important effects of immigration on native wage levels or the wage distribution." And Danny Blanchflower has said that A8 migrants might have helped reduce the Nairu.

So, if immigration has roughly zero effects on average on natives, and is positive for the immigrants themselves - immigrants are humans too, remember - why not just argue for freer migration?

Sarah gives three reasons, none of which convince me.

First, she says, the average zero effect "does not rule out more significant impacts on specific groups of workers (for example in some sectors in particular local areas)." Again, she's right, to some extent. But so what? Pretty much every decent policy has some losers: free speech is bad for lawyers and bigots; counter-cyclical monetary policy is bad for savers, and so on. We don't - or shouldn't - let minorities of losers block other good policies. Why should migration policy be different?

It's certainly not because politicians care especially about the welfare of low-skilled workers. For years, their prospects have been blighted by numerous developments, ranging from poor education through to the rise of China and India and power-biased technical change. There's something nastily hypocritical about a political class which has been indifferent (at best) to the well-being of the unskilled suddenly caring when it comes to immigration.

Insofar as some natives lose from immigration - and they do - the solution is higher in-work and unemployment benefits - policies which I think desirable on other grounds. It is not to stop immigration.

Secondly, Sarah says "migration (including skilled migration) has been part of an economic model that has seen wages at the top end of the labour market become disconnected from those at the bottom." Again, this is true. But it's irrelevant; it's the association fallacy. The fact that a good policy has been associated with bad ones is a reason for ditching the bad and keeping the good - not for doing the opposite, which seems present policy.

Thirdly, Sarah says:

Migration also poses a range of complex policy challenges beyond labour markets and the economy, particularly at the local level ' the rapid population change that can result does affect housing, public services, and community cohesion.

However, we have reasonable evidence that migrants aren't a burden on public services.For example, Jonathan Wadsworth has found they are no more likely to use health services than natives, and Christian Dustmann and colleagues have concluded (pdf):

A8 immigrants' receipt of government expenditures, in terms of benefits and other transfers, is substantially lower than their share of population, so, on balance, A8 immigrants have made a significant net contribution to the UK fiscal system.

There's a reason why I say all this. The "debate" on immigration is currently skewed against the evidence, and against freedom. Personally, I think the role of decent informed people such as Sarah should be not to acquiesce in this bias, but to fight it. We should try to shift the Overton window towards good policy. And this means being less tolerant of those who'd like to sympathize with "concerns" about immigration.