In the suit, Sheriff Tom Dart called Craigslist a public nuisance and accused the site of violating federal, state and local prostitution laws. Specifically, Dart alleged that Craigslist "solicits for a prostitutes ... by arranging meetings of persons for purposes of prostitution."

But Grady disagreed with the sheriff. In a 20-page decision, he listed several dissenting opinions. In short, Grady decided Dart's complaint relies heavily on a few conclusory allegations to support the contention that Craigslist induces users to post ads for illegal services.

Defining the Phrase 'Adult'

The judge wrote, "Even at this stage of the case we are not required to accept those allegations at face value and they are not meaningfully different from the allegations that our Court of Appeals rejected last year ... Sheriff Dart may continue to use Craigslist's web site to identify and pursue individuals who post allegedly unlawful content ... but he cannot sue Craigslist for their conduct."

The court also issued a number of observations in the case. "The phrase 'adult,' even in conjunction with 'services,' is not unlawful in and of itself, nor does it necessarily call for unlawful content ... The same is true of subcategories. Plaintiff is simply wrong when he insists that these terms are all synonyms for illegal sexual services," Grady wrote.

A Publicity Stunt?

"Meritless cases brought by law-enforcement officers, amounting to little more than publicity stunts with little to no chance of success, do little to address the officers' underlying concerns," said Matt Zimmerman, a senior staff attorney at the Electronic Frontier Foundation.

"The problem of sex trafficking is indeed a serious one, as pointed out by both Dart and amicus Coalition Against Trafficking in Women, but as the court pointed out in a footnote, that fact 'does not shed any light on the legal questions before us,'" he said.

Zimmerman said service providers aren't liable because Congress correctly understood that the soapbox should not be held responsible for the speech of others. Just as phone companies are not liable for harassing phone calls, or e-mail software providers for deceptive messages, online message boards like Craigslist are, in most instances, not liable for their users' posts, Zimmerman said.

David Hudson, a scholar at the First Amendment Center, called the decision well-reasoned with respect to the application of Section 230 of the Communications Decency Act.

"Those who believe the law should be changed should address their concerns to Congress and seek an amendment to Section 230 -- something that has not happened to any great degree, I don't believe," Hudson said. "The judge made appropriate use of the Chicago Lawyers case out of the 7th Circuit and the Roommates.com case out of the 9th Circuit."