I think its more about how the Police can stop someone and ask for said immigration card.
We had something like this in Wisconsin several yrs ago, Afro Americans were complaining about being racially profiled by the police, Turned out that they were being pulled over for legal reasons, the case was dismissed.

I think Arizonia should be allowed to enforce this law for a Year and see what the results are. Something does have to be done, our border is a joke, and population density can get nasty.