The underlying theory seems to be that it’s unjust to bar anyone from entering our country. But that’s obviously nonsense. Under international law, we have no obligation to admit anyone to the United States except accredited diplomats. We open our borders to visitors and legal immigrants not because we have to but because we think it’s in our interest to do so.
Now we seem to be moving for a variety of reasons to a situation where we can control our borders and discourage illegal immigration far better than we have been doing for the last three decades.
One reason is the Arizona law that the court upheld, as well as similar laws in other states. Even more important is improved technology and our willingness to use it.