Two things, first you cannot have 50 separate immigration policies (and I guess an extension of that could be the concept of "sanctuary cities" though not sure on this). Unless you had coordination across the entire republic, odds are the immigration laws will be as diverse as our lending laws. In some states we have laws that, in theory, protect the consumer while in others it's a credit predator's dream (ever wonder why so many cards come from certain states?). What you'd end up with is some states where the business lobby wants a heavily exploited and threatened labor pool to those who border on something resembling legislature from certain places in the 1930s (hint hint) to those few progressive places that want something resembling fairness.

But if Arizona gets away with hijacking immigration, this opens up a whole other door to a dangerous land, which gets to my second point. Inside the bowels of the right wing you have what I would consider a Confederate States Renaissance. These range from your anarcho-capitalists to your libertarians to your states-rights racists. The end goal is a federal night watchman state(http://en.wikipedia.org/wiki/Night-watchman_state) which does nothing but insure a modicum of national defense. Once you allow one state to usurp one federal responsibility, what's to stop another from taking something else? Precedent would have been set with a successful Arizona bid.

You may think it's crazy what I'm talking about, but mark my words, first it's immigration, the next will be the interstate commerce clause then well...take it from there. The plutocrats who basically own the majority of assets do not want some federal regulator keeping an eye on them. So they will do whatever is necessary, even weakening the republic, to make sure they pay no taxes, abide to no worker or consumer regulations, and create their own aristocracy in this new mega-plantation objectivist nightmare they want to ultimately impose on us.