By throwing out most of the anti-Latino Arizona immigration law and neutering the rest, the Supreme Court struck a rare blow for fairness and justice. Let’s hope this is the beginning of a streak.

Let’s also hope that Chief Justice John Roberts, who sided with the 5-3 majority in the Arizona case, likes the view from the liberals’ end of the bench. They could use his vote on the health care reform ruling, expected to be announced Thursday.

In a perfect world, the court would have definitively eliminated the most notorious section of the Arizona law: the requirement that police check the immigration status of anyone who is detained. Because of its chilling invocation of police-state tactics, this became known as the “papers, please” provision.

The court ruled that it is too soon to invalidate this part of the law, but significantly narrowed the measure’s scope — and practically dared Arizona officials to step out of line. “This opinion does not foreclose other pre-emption and constitutional challenges to the law as interpreted and applied after it goes into effect,” the court wrote. Translation: We’ll be watching closely.

Other parts of the law were less publicized but equally onerous and un-American. These provisions, happily, are now history.

Even more gratifying is the court’s reinforcement of an obvious principle: The federal government has the responsibility for setting immigration policy, not the states. We do not need — and, thanks to this ruling, will not have — 50 sets of laws specifying who gets to live in this country and who doesn’t.

The Arizona law sought to make it a state crime to fail to have proper immigration papers; in other words, failing to produce the right documents when asked could have subjected a person not just to deportation but to criminal penalties. The court ruled that this was pre-empted by federal law, which imposes no such sanctions.

Arizona’s draconian statute also made it against the law for an undocumented immigrant to look for work. The court noted that existing federal law already addresses the employment issue but specifically puts the onus on employers, not workers.

It is “illegal for employers to knowingly hire, recruit, refer, or continue to employ unauthorized workers … and requires employers to verify prospective employees’ employment authorization status,” the court said. “The correct instruction to draw … is that Congress decided it would be inappropriate to impose criminal penalties on unauthorized employees.”

And in a provision that, to my thinking, was even more oppressive than “papers, please,” the Arizona statute gave police the authority to arrest anyone — without a warrant — suspected of some “public offense” that makes the person liable to deportation. The court recognized, quite logically, that this is a license for police to arrest suspected illegal immigrants indiscriminately, based solely on the possibility that they might be here without the proper documents.

As the court noted in striking down this provision, “The result could be unnecessary harassment of some aliens (for instance, a veteran, college student, or someone assisting with a criminal investigation) whom federal officials determine should not be removed.”

The majority opinion, written by Justice Anthony Kennedy, points out something that many who seek to participate in the immigration debate fail to understand: “As a general rule, it is not a crime for a removable alien to remain present in the United States.”

That’s right. It’s not a crime for “illegal” immigrants to live and work here without the proper documents. By “here” I mean all 50 states. The United States is one country with one immigration policy, and the Supreme Court means to keep it this way.

That’s why analysts who see this as a split ruling with “something for both sides” are wrong. The Obama administration won across the board on its central contention, which is that Arizona was trying to usurp a federal prerogative. This has huge implications for the other states, such as South Carolina and Georgia, that are also trying to design their own immigration policies.

There are political implications as well. Mitt Romney, who is struggling to reduce President Obama’s huge lead among Latino voters, once referred to the Arizona law as “a model.” Romney reacted to Monday’s decision by reiterating that “each state has the duty and the right” to protect the nation’s borders.

Actually, no. Romney should read the ruling.

Eugene Robinson’s e-mail address is eugenerobinson(at)washpost.com.