A fundamental principle of law is that it should protect the innocent. Of all the damage made possible by Gov. Jan Brewer's signature on Friday to Senate Bill 1070, the worst is not the harm to the world's judgment of Arizona or to this law's economic consequences.

The worst effect is its grave potential for causing harm to innocent, taxpaying American citizens who no longer can feel certain of the law's blindness.

That is the terrible harm of it. SB 1070 lifts the blindfold of Lady Justice and commands her to see one different from the other, irrespective of innocence. Brewer's televised signing ceremony for this harsh, unnecessary legislation constitutes the low point of an administration we have come to admire for its often surprising grit in the face of hard times. We held out hope for more.

Whether Arizona pays a price for indulging the whims of state Sen. Russell Pearce, R-Mesa, is no longer the issue. We are paying a price. Not since the dismal days of our nationally infamous fight over a holiday to honor the Rev. Martin Luther King Jr., has the profile of Arizona descended this low.

It isn't as though the potential consequences of this law are unapparent. We have been down this road before.

The terrible "Chandler Roundup" of 1997 still stands as a warning of what may lie ahead. Then, like now, local police officers demanded proof of citizenship of people they suspected might be in this country illegally. Scores of American citizens lacking "papers" were cuffed. An international outrage erupted. SB 1070 opens the door to the return of those brutal neighborhood-dividing days.

Also Friday, Brewer signed an executive order to establish law-enforcement training she hopes might mitigate the worst potential effect of SB 1070, racial profiling. A nice gesture, certainly. But a few hours of additional training is unlikely to alter the now-evolving relationship of local police to their citizenry, a relationship made infinitely more difficult and attenuated by the signing of SB 1070.

We are not blind to the political challenge facing Brewer. She is a Republican facing stiff competition in an approaching election, and not signing SB 1070 likely would have doomed her candidacy.

That is her political problem, however. Not Arizona's.

She is certainly correct on one count. The widespread popularity of this punishing legislation would be far weaker if Washington, D.C., would act seriously to do its duty regarding Arizona's southern border.

This is very bad law. And this is not the end of the fight against it.