I have to admit, I had it all wrong. I thought opponents of Arizona's new law just hadn't read it for themselves.
That's why, in a previous post, I explained that Arizona law enforcement has not been given any new, broad powers to demand "papers, please," of random passersby; and that legal resident aliens were already required to carry documentation with them at all times - and had been so required under Federal law since FDR was president.
Under the new law, the circumstances under which police officers may seek documentation of immigration status are bounded by "lawful contact" and "reasonable suspicion," exactly like every other offense on the books.
These two concepts are well-defined through generations of law and precedent. If you can't accept those as the bars law enforcement has to clear before they can start poking around in your business, then you don't really object to the Arizona law per se, you object to any enforcement of immigration laws.
I guess that should have been obvious to me, as it falls in line with my cynical view of the political left. They do not care about facts. They will say anything to get their way. Once again, they are doing it. They know perfectly well there are no draconian measures in Arizona's law; they know it is not fascist or racist or extreme.
But they also know it will result in enforcement of existing immigration laws, and that's what they really oppose.