It takes just one law to begin the alienation process of a group of people. It takes just one law to allow local police and reasonable suspicion to stop anyone that appears to be Hispanic and ask for their immigration papers.
First we single them out, we identify them, and then we deport them. Sound familiar? When Hitler came into power he first singled out the Jews for draining the nation of its resources, then he implemented curfews, then soldiers could stop anyone on the street that appeared to be Jewish to ask for their identification. Then millions of Jews were deported, brutalized and murdered.
Read the CNN article which provides a good overview of the fears that this law has already sprouted in