In the world as Supreme Court Justice Antonin Scalia imagines it, anti-abortion advocates resemble Eleanor McCullen, a self-described “mother and grandmother” who stands outside a reproductive-health clinic in Boston and attempts to gently “counsel” approaching women out of getting an abortion.He also sees lawmakers and judges conspiring to silence the voices of those like Ms. McCullen by establishing buffer zones on public sidewalks around those clinics.

Out in the real world, of course, all anti-abortion advocates are not Ms. McCullen, and buffer-zone laws like the one in Massachusetts, which set a 35-foot area around clinic entrances, are a considered response to a decades-long threat to public safety, largely in the form of harassment, physical intimidation and worse by people opposed to abortion.Yet on Thursday the Supreme Court, in Mc Cullen V.Coakley, struck down that law for violating the First Amendment. Massachusetts’s buffer zone, it held, burdened “substantially more speech than necessary” to protect public safety. If individual protesters try to block a clinic entrance or harass a prospective client, the court said, Massachusetts already has laws on the books to deal with them.

This ignores what actually happens on the ground. As the factual record of the case made clear, Massachusetts has, like most states, endured a long and sometimes violent history of protest at reproductive-health clinics, including the 1994 murders of two Planned Parenthood workers by an abortion opponent.

As both opponents and defenders of abortion rights have converged on the clinics over the years, initially peaceful protests have escalated into shoving matches, with women caught in the middle.

An earlier law setting a “floating” buffer zone of six feet had proved impossible to enforce, police officers testified. “Everybody is in everybody’s face, no matter what,” one captain said. “It’s almost like a goalie’s crease out there.” The 35-foot buffer, the police said, was by far the most effective way of keeping the peace, maintaining public safety and still respecting freedom of speech. The justices have firsthand experience with striking that delicate balance. The Supreme Court building’s own buffer zone, which includes its vast plaza, and is far larger than 35 feet, prohibits “demonstrations, picketing, speechmaking,” or any other conduct that is “reasonably likely to draw a crowd or onlookers.” Yet all manner of viewpoints are expressed without difficulty every day on the sidewalk in front of the court.

The McCullen ruling, written by Chief Justice John Roberts Jr., was, surprisingly, unanimous, but Justice Scalia correctly called it a “specious unanimity,” and filed a fuming concurrence in which he agreed only with the final outcome.

He was upset by the majority’s assertion that the law did not discriminate against the content of any speech or against any speaker’s viewpoint. But what appeared to infuriate Justice Scalia most was the court’s failure to understand that the “obvious purpose” of buffer-zone laws is to “protect” women from having to hear any speech against abortion. He would have also overturned the court’s ruling in 2000 that upheld a Colorado law creating a smaller, floating buffer zone around health clinics.

Chief Justice Roberts’s opinion does not discuss that ruling. It narrowly focuses on the law’s challengers, whom it characterized as offering “counseling and information,” and engaging in “personal, caring, consensual conversations.” But paper leaflets and polite words are not the real threats women face in trying to exercise their constitutional right to an abortion.