Bruce Charlton sensibly asks (in a comment to this post ):
Isn’t illegal immigration more equivalent to smuggling than to free trade?
I would favour easier, cheaper and quicker regulation of immigration, which would need to be coupled with general reforms to cut back on welfare and making it easy to work legally, repealing the minimum wage etc.
But I find it hard to see how mass scale law-breaking can be ignored without serious knock-on problems.
I respectfully disagree with Mr. Charlton — or, rather, I submit that he (like so many other persons) is inappropriately distracted by immigrants’ “legal” status.
A critical distinction in Anglo-American law is that between actions that are malum in se  and actions that are malum prohibitum . Some actions are malum in se — wrong in themselves. Examples are murder, rape, theft, and fraud. These actions are now formally prohibited by legislation, but their wrongness — indeed, their very illegality — exists independently of legislative prohibition. If, say, the Virginia legislature were to repeal its statutory prohibition on murder, murder would still be wrong and criminal in Virginia. Murderers would still be wrongdoers and criminals. If the State government refused to punish such criminals, people would do so privately.
Other actions are malum prohibitum — “wrong” merely because the government proclaims these actions to be wrong. One example is avoiding taxes. If Uncle Sam tomorrow abolishes the federal income tax, failure of Americans to send money to Washington would be neither wrong nor criminal, and persons who send no money to Washington would not be regarded by their neighbors and co-workers as despicable louts whose company should be avoided.
To attach the label “criminal” both to persons who commit actions that are malum in se and to persons whose only wrongdoing is the commission of actions that are merely malum prohibitum is to use language confusingly. It is to dilute the scorn and loathing that true criminals deserve. After all, if someone whose only offense is to cross the U.S.-Mexico border in search of a job is a criminal, what is a shoplifter or a child-beater or a murderer?
Looked at differently, to call “criminal” those persons whose only offenses are merely malum prohibitum is unfairly and inappropriately to tar them with the scorn and wariness that is deserved only by persons who commit genuine offenses against others.
And such language clouds and confuses the political debate. Because most persons understand the word “criminal” to indicate an individual who, to one degree or another, is harmfully anti-social, calling immigrants who are in the U.S. without official government permission “criminal” gives the impression that these people are all harmfully anti-social. But that impression is emphatically false (unless you include in your definition of “anti-social” the desire for a better life and willingness to compete for jobs).
There is a legitimate debate over how open America’s borders should be. But that debate today is far too soiled by those persons who think that merely calling “illegal” immigrants “criminals” settles the matter. It does not. “Illegal” immigrants are “criminals” only because government policy declares them to be — in the same way that persons openly practicing Christianity or Judaism in Soviet Russia were “criminals” only because government policy declared them to be. The contours and specifics of this policy are precisely what is at issue in the debate over how widely open U.S. borders ought to be. This debate should be on the economics and the national-security issues raised by immigration; it should not be confused by the confusing (and often self-serving) application of the term “criminal” to persons who come to America without Uncle Sam’s permission — permission that is very difficult to get.