Arnold doesn’t share my conditional jubilation over Obama’s semi-amnesty.  Arnold’s in blockquotes, my replies follow.

Even if you want open borders, I am not sure that this is how you want
your goals accomplished.

I see no other politically possible way this could happen.  Waiting for the median voter to come to his senses is like waiting for Godot.

My reading of the policy is that the President
is nullifying a law by refusing to enforce it. That is a precedent
that could come back to haunt us.

I say the laws on the books are so overwhelmingly wrong that even random Presidential nullification would be a huge expected improvement. 

My question for Arnold: What’s the best law any future President is likely to nullify due to Obama’s precedent?  I just don’t see this slippery slope leading anywhere we should fear to slide.

I should point out that immigration laws already are very weakly enforced. In fact, when I drew up a list of legamorons (laws which, if they were rigorously enforced, would cause extreme disorder), immigration laws were number one on my list.

Hardly.  The U.S. forcibly exiles over a million illegal immigrants almost every year; as I’ve explained before, the legal distinction between “removal” and “voluntary returns” is minor.  The fact that coyotes in Mexico – our closest Third World neighbor – charge about two years’ salary shows that U.S. enforcement is very draconian indeed.  As economists, moreover, we shouldn’t forget that immigrants drastically change their behavior (e.g. never driving) to reduce their risk of deportation.  If you know anyone who lives with this fear – and I do – it’s horrible.

Perhaps you can think of the President’s move as analogous to civil
disobedience–it is a way of calling attention to a law you don’t like.
However, I think that civil disobedience is much more defensible for an
ordinary citizen than it is for the President of the United States.
Ordinary citizens need ways to publicize their opposition to laws. The
President can publicize his opposition just by giving a speech.

“Calling attention” to unjust laws is one of the weakest rationales for civil disobedience.  The main point of disobeying an unjust law is to reduce its number of victims by one.

In a better world, I would rather have seen the President give a ringing
speech in favor of changing a law than announce an intent not to
enforce it.

Obama did give a speech.  Not a bad one, I might add.  But if Obama only gave a speech, nothing would have changed.  Now it seems hundreds of thousands, if not millions, will win their basic human right to accept a job offer from a willing employer.  And even if Romney wins, it sounds like he’ll treat his rival’s semi-amnesty as a fait accompli.

“Too good to be true”?  Maybe.  “You’ll be sorry”?  Highly unlikely.