Just to be totally clear on the grounds of my debate with Tim about immigration: I’m not particularly an immigration restrictionist. Indeed, I see good arguments, economic and compassionate, for a relatively liberal immigration policy. I do not think our current immigration policy – large-scale illegal immigration combined with highly confusing and economically sub-optimal rules for legal immigration – makes much sense on pretty much any metric. In general, I would say that immigration should presumptively increase global income, because if an immigrant were not more productive in his new home he would not undertake the transaction costs to move, and some of that increase in productivity should be captured by the country to which he moves.
My point was a simple one: economic arguments about what will increase global wealth, and arguments from compassion about helping people from poor countries, are not libertarian arguments; and, moreover, I do not accept the argument that immigration restriction is as such an immoral position, comparable to supporting apartheid. I think the restrictionist position is perfectly valid. Some of the reasons why I think it is valid would be reasons that Tim might reject because I’m not a libertarian. So the focus of my debate with him has been over whether immigration restriction contradicts libertarian principles as such (I don’t think it does) or is patently immoral because it restricts the liberty of the prospective immigrant without proper justification (I don’t think it is).