For the record, I do think that opening the borders fully and completely immediately wouldn’t produce very good results. The rush would overwhelm public and private services in most of the border states; they simply wouldn’t have time to adjust. There would be serious overcrowding, a drastic shortage of lodging, and probably serious violence coming from communal upheaval and contest for increasingly scarce resources. As Mises, Rothbard, and Hoppe all correctly point out, time is a factor in all production.
I think, though, that I can also say that the poor results that immediate opening would produce is a result of immigration restrictions. Many Mexicans, for instance, don’t want to come to live in America full-time. They want to work in America and live in Mexico, or they want to work in America during seasonal periods of demand (harvests and planting, especially) and return to Mexico when the labour crush is over. Immigration policies seriously botch what would otherwise be a very normal, regular, seasonal migration back and forth between Mexico and America. Immigration restrictions actually encourage people to come and stay who really don’t want to do so.
Immigration policy has further problems. Whenever the state tries to restrict peaceful travel and commerce, black markets pop up to supply that demand. However proper the commerce might be, most of the people involved in black markets are lousy human beings, many are exploitative, and a serious portion are outright criminals. The black markets in narcotics are a case in point: narcotics trafficking is not, in and of itself, a crime, but most of the people involved in the trade are criminals (and the rest are unsavoury, to be charitable). No openness, no transparency, no appeal to legal remedies: it’s no wonder that immigrants are dying off left and right.
Immigration policy, itself, has created the unfortunate but likely on-rush that would follow an abrupt end to immigration restrictions. Whether out of respect for the law, out of fear of the immigration enforcers, or out of fear of the unsavoury characters (coyotes) involved in immigrant smuggling, a number of people who have long-desired to come to this country have not. They are waiting, wherever they are, hoping for an opportunity to do so but afraid of the costs. Had the borders been open forever, these people would have come whenever they could have afforded bus fare to get here. But since the immigration policies kept them out, they’ve been bottled up, waiting and hoping.
This, in part, answers some of the utilitarian objections made about open borders. Yes, if Switzerland opened her borders completely tomorrow, very likely it would suffer a rush of people who have been dying to get in. Ditto most wealthy countries. However, if their borders had always been open, people would have streamed in over many years. When people come in a steady stream, they are more easily integrated into the new society than would a large group of people who show up roughly simultaneously. In a free society, a steady stream of people who arrive come to be socialised and to understand why their new country is so much better than their old one. It’s true that, if they opened the borders tomorrow, a rush of new immigrants would show up that would never and probably could never be socialised. However, if those people had been able to come all along, the socialisation process could have easily kept up.
As with anything else, state interference in the free movement of people across borders creates many more problems than it solves.
(My father’s family came to this country to escape the wars for Irish independence in the early 20th century. My mother’s family came to this country to escape English persecution of Methodists and Brownians in the 17th century. I love this country for giving them an opportunity to escape, build their lives, and thrive.)