A commenter on a previous post asks: why is immigration such an obsession on the left? To answer this question, let's first note that the free market right should be strongly opposed to immigration controls.

This is simply because immigration is a matter of freedom. Restrictions on immigration deny people the freedom to live where they want; employers the right to hire whom they want; and landlords the right to let their property to whom they want.

I'm old enough to remember when rightists did indeed assert these freedoms. During the Cold War one of the biggest accusations against the USSR was that it denied its subjects the right to emigrate. And Norman Tebbit's famous 1981 speech in which he praised his father who "got on his bike and looked for work" could be regarded as applauding free movement: if it's praiseworthy to get on your bike and look for work, shouldn't we also praise those who get on boats and planes to do so?

Few rightists today, however, proclaim the rights of migrants. Yes, some do such as Bryan Caplan and Sam Bowman. But such men have far less influence than their intellect and integrity merit.

This poses the question: why are so many Conservatives who have traditionally asserted the virtues of free markets so silent about the merits of migration?

You might say it's because freedom is a matter of degree and must be limited to accommodate other goods.

But this won't do, for three reasons:

- Many of those who want immigration controls also want economic freedoms to be restricted in other domains. Many Ukippers, for example, support (pdf) price controls and nationalization.

- A big case for freedom lies in the invisible hand - the idea that aggregate welfare increases when each individual is free to pursue his own goals. If you're going to deny the benevolence of the invisible hand in the domain of immigration, it's difficult to assert it in other domains, especially as the empirical evidence (pdf) suggests that (in economics at least), free migration is indeed benign.

- The goods with which immigration is alleged to conflict aren't those which free marketeers value highly. Let's concede that immigration does undermine social cohesion (something which I doubt). So what? Cohesion is a collectivist ideal which shouldn't appeal much to free market individualists.

It should, therefore, be the right that is championing the virtues of immigration at least much - if not more so - than the left. So why isn't it?

One possibility is that the right never truly believed in freedom anyway. They merely used the it as a stick with which to fight the ideological Cold War, and as a means of attacking workers. Now that these uses are no longer necessary, rightists are exposed as the freedom-hating bigots they've always been.

But perhaps there's something else, or another way of expressing the point. The Tory party has for most but not all of its history been highly pragmatic, capable of ditching principles or prejudices when electorally necessary. It has managed to retreat from the free market rhetoric of Thatcher without great turmoil; Osborne's embracing of the minimum wage, for example, caused little fuss.

Much of the left, however, is more idealistic. And herein perhaps lies the answer to the question: why is it preoccupied with immigration? It's because immigration embodies a conflict between principle and practicality: free(ish?) migration is good policy (from both left and right perspectives), but electoral disaster. The left feels this dilemma but the right - especially the populist element thereof - is less troubled by it.