Several commentators suggest that the U.S. federal government should build a better barrier along its border with Mexico. They explain that a curtain of steel, electronics, and armed guards would protect U.S. citizens from illegal immigration. Maybe it would, maybe it wouldn't. I don't intend to take up that question, here. Nor do I here aim to settle whether and to what extent we need protection from immigrants. I want only to make one small point: Any wall good enough to keep people out of the U.S. will also keep them in.
Does the present, tattered, "tortilla curtain" thereby threaten to become a new and coldly efficient one? One of the few bloggers to address that concern, self-proclaimed "Classical Liberal Writer," Ilana Mercer, discounts the idea. She attributes it to a few unattributed "hysterics" who "claim the totalitarian state won’t let its citizens exit," but who fail to appreciate the ample freedoms of the U.S. because they've "never experienced totalitarianism."
Even in her unsympathetic account, however, the objects of Mercer's scorn have a point. You don't have to suffer totalitarianism personally to observe that it tends to bar freedom of exit. You need only read books about communist East Germany or news accounts about communist North Korea. Nor is it inconsistent to relish your extant freedoms even as you worry about their loss. Quite the contrary.
It would court hysteria, granted, to claim that every step towards improving the U.S. Border Patrol takes us one step closer to Berlin, c. 1970. Not being hysterical, I'm not claiming that. I mean only to observe that walls work both ways. Consequently, no calculation of the utility of hardening the U.S.-Mexico border should ignore the costs of trapping in Northerners.
Restricting undocumented traffic across the U.S.-Mexico border would make it harder for immigrants here illegally but temporarily to return home. The consequences of tightening the border might thus give even xenophobes pause. I'm more interested, though, in the safety valve that illegal emigration affords to U.S. citizens.
Many miscreants who run for the border—the murders, thieves, and con artists—do not deserve to make it. Some arguably do, though. Not every U.S. law promotes justice (see, e.g., those supporting the Drug War), nor is every convicted criminal guilty (see, e.g., those imprisoned on false evidence). And even if those sorts of law-breakers don't attract your sympathy, keep in mind that the law could change, making illegal acts once tolerated (such as owning firearms) or even encouraged (such as freely funding political speech).
We cannot expect perfection in any human institution, much less one that, like the law, wields coercive power. We can, however, aim for a rough balance of imperfections. Our moderately porous border with Mexico arguably helps to protect us from totalitarianism at home. Thanks in part to the freedom of exit it affords us, we enjoy what we might call "partialarianism"—incomplete political rule. Tightening our border with Mexico might put our partialarian form of government at risk, making the perfect wall an enemy of the good.