Free market supporters of immigration controls often quote Milton Friedman in support of their position:

“There is no doubt that free and open immigration is the right policy in a libertarian state, but in a welfare state it is a different story: the supply of immigrants will become infinite.”

On the face of it, this is a powerful argument for restriction. As I’ve noted in the past, whether we like it or not people are dependent on state institutions like the NHS and it would be a bad thing for those things to crumble without the reforms that make market-based alternatives viable.

But are things as clear as they seem? Elsewhere, Friedman also said:

“Look, for example, at the obvious, immediate, practical example of illegal Mexican immigration. Now, that Mexican immigration, over the border, is a good thing. It’s a good thing for the illegal immigrants. It’s a good thing for the United States. It’s a good thing for the citizens of the country. But, it’s only good so long as it’s illegal.”

I think Friedman vastly overstates his case in his final line (it’s only good if it’s illegal?), and empirically he seems to be mistaken (the fiscal contribution of immigrants is usually positive in general, and has been positive in the UK in particular) but still, let’s take his point as given. Does that make immigration controls the best option?

No. There are ‘keyhole solutions’ we can implement instead – that is, solutions that are specifically designed to address the supposed problems that go with open borders.

We could require that immigrants post bonds priced according to the average cost to the state of someone of their age. We could require immigrants to provide for their own health insurance, unemployment insurance, education, etc. We could restrict the use of the NHS and other state services to immigrants who are working. And so on. The point is that most of the problems associated with immigration are not best solved by restrictions on immigration. Don't use a sledgehammer to crack a nut.

Well, OK, but we are where we are. Those solutions are nice in a think tank fantasy-land, but they’re never going to happen, you might say. (Well, not with that attitude, they're not!) For the sake of argument, what if these keyhole solutions were irrelevant and Friedman was empirically correct?

In that case, his point about illegal immigration being the best kind of immigration – and indeed, a net positive overall – might really be worth thinking about. As Will Wilkinson has argued, people who follow Friedman on immigration should then argue not for restrictive immigration controls, but restrictive immigration laws paired with a toothless Border Agency, or one simply told in practice to ignore these laws. (Much as most decent police officers ignored anti-sodomy laws for some time before those laws were repealed.)

So maybe that’s a Friedmanite ‘keyhole solution’ for people concerned about immigrants sucking the welfare state dry: keep immigration laws the way they are, but shut down the UK Border Agency and treat the laws as the silly anachronisms they are.