Back in January, Chief Justice John Roberts did not ask one question during oral arguments in a case concerning whether a Massachusetts law that provides a 35-foot buffer zone around the entrances of abortion clinics violated the First Amendment.

That was a very rare thing to happen.

Perhaps, he already knew how he was going to rule and wanted to allow other justices time to ask questions. On Wednesday, he issued an opinion in McCullen v. Coakely, invalidating the law, but leaving open the possibility that states could pursue other alternatives to address the issue.

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A unanimous court agreed the law should be struck down - but only the liberal justices agreed with Roberts' reasoning.

The Massachusetts law makes it a crime to "enter or remain on a public way or sidewalk" within 35 feet of an entrance, exit or driveway of an abortion clinic."

In his opinion, Roberts said that the buffer zones in Massachusetts "burden substantially more speech than necessary to achieve the commonwealth's asserted interests."

He added, "The Commonwealth has not shown that it seriously undertook to address the problem with less intrusive tools readily available to it. Nor has it shown that it considered different methods that other jurisdictions have found effective."

But he also added this key line: "We thus conclude that the Act is neither content nor viewpoint based and therefore need not be analyzed under strict scrutiny."

What does that legalese mean?

"The key fight between the progressive and conservative justices is whether laws like these are specifically targeted at anti-abortion protestors. The compromise at the heart of the Chief Justice's opinion is in holding that these laws are not so targeted, but that the Massachusetts law is invalid anyway because it is excessive, " said Stephen I. Vladeck of American University Washington College of Law.

The case was brought by Eleanor McCullen, a 77-year-old grandmother who seeks to peacefully reach women who may be contemplating an abortion. McCullen stands on public sidewalks near abortion clinics in Massachusetts, her lawyers say, to reach "a unique audience, at a unique moment, in a compassionate and non-confrontational way."

McCullen has said her efforts have been stymied since 2007 with the passage of the law. She was delighted with Wednesday's decision: "Today's ruling means I can offer loving help to a woman who wants it, and neither of us will go to jail for the discussion," she said.

Massachusetts Attorney General Martha Coakley had defended the law, saying it was necessary after other federal and state laws failed to solve the problem of demonstrators blocking public access to clinics. She said it was a matter of public safety, not speech. After the decision, she said, "We are not going to give up our fight to make sure women have safe access to reproductive health care. We will utilize all of the tools we have available to protect everyone from harassment, threats, and physical obstruction. I will work with the Governor, Legislature and advocates to explore additional legislative tools that also meet the court's requirements."

But women's rights groups condemned the ruling.

"This decision shows a troubling level of disregard for American women, who should be able to make carefully considered, private medical decisions without running a gauntlet of harassing and threatening protesters," said Cecile Richards, president of Planned Parenthood Federation of America.

Justice Antonin Scalia (joined by Justices Anthony Kennedy and Clarence Thomas) and Justice Samuel Alito wrote separate concurring opinions, saying they would have gone much further than Roberts.

"Today's opinion carries forward this Court's practice of giving abortion-rights advocates a pass when it comes to suppressing the free-speech rights of their opponents," Scalia wrote.

Scalia disagreed with Roberts' opinion that the speech at issue was "content neutral" and thus does not trigger closer scrutiny from the court.

"Protecting people from speech they do not want to hear is not a function that the First Amendment allows the government to undertake in the public streets and sidewalks," he wrote.

Scalia was also concerned that the Massachusetts law allowed clinic employees to escort prospective clients into the zone, even though McCullen was not allowed in.

"Are we to believe," he wrote, "that a clinic employee sent out to 'escort' prospective clients into the building would not seek to prevent a counselor like Eleanor McCullen from communicating with them?"

ABC's Jake Lefferman contributed to this report.