Last week, Theresa May spoke of wanting to increase social mobility, so that "it's your talent and hard work that matter, not where you were born." This week she wants to restrict immigration. There's a massive contradiction here.

I say this for a trivially obvious reason - that migration is a fantastic form of social mobility because it raises people out of poverty. Orley Ashenfelter, for example, shows (pdf) that real wages at McDonalds are seven times higher in the US than in India: Indians are poorer than westerners not because they're less talented or lazier but because India is a poorer country.

Allowing people to migrate would allow them "to go as far as their talents will take them", which is what Ms May wants. Immigration controls, on the other hand, mean that "where you were born" will, in millions of cases, condemn you to life-long poverty.

It's obvious, therefore, that anyone who is sincere about wanting everyone to have a "fair chance to go as far as their talent and their hard work will allow" should favour open borders.

So, why doesn't Ms May?

One possibility is that she simply hasn't thought about it much - though what does that tell us about politics?

There are some nastier possibilities. Maybe she doesn't want real meritocracy but merely a sham appearance thereof that would serve to legitimize inequality.

Worse still, it might be because of the same sort of hypocrisy that leads Europeans to want rights of free movement for themselves but not for others. Whereas we British have "legitimate concerns" that politicians must address, foreigners are a problem to be managed. Chris Bertram say this is racist. I'd add that it looks like feudalism: the highborn (those of us born into rich countries) have a right to preserve and increase our wealth, whereas the lowborn must be kept in poverty by the use of force.

Maybe I'm being too harsh here, though. Perhaps the free migration that would increase social mobility would incur some costs - not so much economic as cultural or just the sort of sense of disquiet that accompanies rapid change. And perhaps members of nations have obligations to each other that justify excluding outsiders, even though these nations are in part merely imagined communities: this is one issue in the debate (pdf) between the Rawls of The Law of Peoples (pdf) and cosmopolitans.

I don't want to take sides on this: FWIW my instincts are for open borders but I see that this would have huge practical problems. My point is merely that immigration restrictions are a massive barrier to social mobility, meritocracy and the alleviation of absolute poverty, and should therefore be supported if at all only with a heavy heart and misgivings about their massive cost. What I find hard to understand or forgive is that so few of their advocates seem to feel such misgivings.

Another thing: you might object that politicians have a duty to their voters, not to the world. This is too glib: can people really legitimately incur duties to harm others? Should we, for example, respect a hired killer's duty to carry out his employers' orders?