This is no different than if the EU State of Poland mobilized its laws and cops to protect itself from militias from Russia.
Actually it is very different. We are the f'ing USA; we have a constitution and a supreme court that specifically says this type of action (arresting/detaining people without probable cause) is illegal and a violation of civil rights.
It will be a short matter of time before this law is declared unconstitutional. I have no problem with the State of Arizona trying to deal with the immigration problem, however rounding up and detaining people is way WAY out of line, and making people carry their papers at all times or else go to jail is repugnant.