Thank you for the link, Michael. Good article! I found especially interesting the comment that most people nowadays do not know the difference between immigration and naturalization! But good point about the Constitution addressing naturalization but not immigration, leaving to the states the option to deal with the latter.
However, as an aside, it would seem to me that a much bigger constitutional issue in the Arizona law is the 4th Amendment's searches and seizures clause. Also, to consider the commerce clause, maybe.