Today, McMaster sent a letter to CEO Jim Buckmaster threatening the site's management with criminal prosecution if it doesn't remove ad categories that allow for "the solicitation of prostitution and the dissemination and posting of graphic pornographic material" by May 15.
It's not at all clear why McMaster thinks he can bring criminal charges against the site relating to pornography, when the First Amendment protects people's right to post such material (provided it's not obscene).
As to the allegations that Craigslist facilitates prostitution, the site has a good legal argument that the Communications Decency Act immunizes it from liability for material posted by users. Courts throughout the country have rebuffed litigants who have attempted to hold Web sites responsible for the criminal acts of users.
But, if nothing else, law enforcement officials can at least make trouble for Craigslist if they want to. Already the site is defending itself in a lawsuit filed by the Chicago sheriff.
In fact, the site just this week filed a motion asking the court to dismiss that case. Craigslist argues that courts have repeatedly held that the Communications Decency Act "protects online service providers from suits seeking to impose liability on them for harmful and/or unlawful communications that originate from the users of the services."
Last year, a federal appellate court in Chicago ruled that the same law protected Craigslist from liability for illegal apartment ads.
Craigslist also argues that Illinois law prevents government entities, like a sheriff, from suing for damages stemming from the cost of policing.