Why all the fuss about Arizona's SB 1070?

I'm astounded at the May Day rallies in support of illegal immigration, both on the streets and in the media.

I do agree with some of the ideas behind these rallies, though. For instance, I agree that the US policy on this has been wrong for decades, and that Mexico's is right. We should clearly do what Mexico does: send Mexican criminals across the border, rather than encourage them to stay.