People who care about things like evidence and prosperity have pointed out that proposals to limit EU immigration after Brexit are bad for the economy. It's not sufficient, however, merely to point out facts. We must also ask: why - of all the false beliefs it is possible to have about the economy - is the idea that migrants significantly depress wages so widespread and entrenched?

In some cases, of course, it's simply a rationalization of hostility to migrants. Some people would hate immigrants whoever they were and whatever they did. The claim they do economic damage is a cloak for such feelings.

There are, though, more respectable motives. I don't think it's unreasonable to feel a little uncomfortable about high migration on the grounds that it might disrupt our sense of home or that diversity might in the long-run undermine social solidarity and hence perhaps (pdf) support (pdf) for redistribution; it's an awkward fact for leftists that several egalitarian nations (such as the Nordics, Japan and South Korea) tend to be more ethnically homogenous than less egalitarian ones such as the US*. It's easy for such people to commit a form of halo effect, and fear that because migration might be bad in some senses it is also bad in others.

Nor must we overlook folk economics. Very many people can tell stories along the lines of "since a lot of Poles arrived my wages have fallen." And these have a simplistic appeal: increased supply means lower prices, doesn't it?

To counter these stories we need not just a technocratic appeal to the facts but to point to mechanisms which offset those stories - such as that immigration also increases demand. People are bad at making connections about the economy. They must be shown how to do so, but there are no institutions which do this.

I'm not sure, though, that these explain the Tories' urge to blame migrants for stagnant real wages, and they certainly don't justify Ms May's refusal to even consider evidence about the matter.

Instead, I suspect something else is going on. The Big Fact about the economy is that we're now seeing the weakest trend productivity growth since the early days of the industrial revolution; it's this that is largely responsible for flat real wages. Any non-risible political party must have some sort of analysis of this.

The Tories, however, not only do not but cannot offer such an analysis. Obviously, they cannot blame austerity. Nor can they blame trades unions or red tape, as they did in the 1980s. And nor can they blame capitalist stagnation or managerialism. This leaves immigrants as pretty much the only possible scapegoat.

I've said many times that capitalist stagnation fuels hostility to immigration. The Tories exacerbate this because their political and intellectual limitations mean they cannot do anything else but blame immigrants for stagnant real wages. In this sense, curbs on immigration have something in common with Jacob Rees-Mogg (Roderick Spode masquerading as Gussie Fink-Nottle) being considered a half-credible leadership contender: both are signs of a deep intellectual and political malaise in the party.

* My sympathy for open borders - like my anti-managerialism - perhaps owes at least as much to my Hayekian as my Marxian influences.