Kerry Howley's "Guests in the Machine" (not yet online) in the January 2008 Reason is a thoughful summary of the immigration debate.
"Guest worker programs mean legal inequality, tight government controls, and sometimes terrible abuses. They are also the best hope many of the world's poorest people have of improving their lot in life. ... The moral calculus, then, is to be weighed between the welfare of potential workers and the preservation of an idealized narrative. Does it reflect better on the American character to lock people out than to permit them entry on limited terms? Guest worker programs do clash with deeply held mythologies about our relationship to the global poor. We live in a state of relative poltical equality nested awkwardly within a deeply unequal world, and it can seem better, kinder, to keep the inequality outside, walling it off and keeping our hands clean. Perhaps American exceptionalism, like a dress too precious to be worn, is a value too dear to expose to the rest of the world."
Heady stuff that contrasts with the presidential candidates' blather. What we hear from them is often depressing. Mike Huckabee has been able to take some high ground, citing religious reasons to not bar children of immigrants from state colleges. Never mind the economic arguments, it may take a credible Christian conservative to resist nativist populism. The left-leaning Barack Obama could (perhaps) separate himself from the pack and get the serious consideration of libertarians of all stripes if he decides to reach for the high ground on this issue. What good is charisma if it is not used?