TNC counters Frum:

Defenders of the law will say that police still have to stop you for something, and they still have to "suspect" that you did something.

Forgive, but I don't find that comforting. Amadou Diallo is dead because the police "suspected" he was drawing a gun. Oscar Grant is dead because the police "suspected" he needed to be tased. My old friend, Prince Jones, Howard University student and father of a baby girl, was  murdered by the police in front of his daughter's home because police "suspected" he was a drug-dealer. (The cop was not kicked off the force.) Only a year ago, I was stopped in Chelsea, coming from an interview with NPR, because police "suspected" I was the Latino male who'd recently robbed someone. 

This comes down to police power, and how comfortable you are with its extension. George Will, in a bit of populist demagoguery, implies that the critics of the Arizona law are people who only know illegal immigrants as cheap labor. But I suspect Will mostly has the exact same relationship with illegal immigrants. Moreover, I suspect that he only knows the police as the kind of Officer Friendlies who only arrest "the bad people."