Is Craigslist a common carrier?

The news today is that Craigslist has, without explanation, stopped running ads for adult services.  This follows a letter from 17 attorneys general asking Craigslist to remove their adult services section, something that the states cannot legally require Craigslist to do.  In the words of Ryan Calo, a senior research fellow at Stanford Law School's Center for Internet and Society (as quoted in today's New York Times) “What’s happened here is the states’ attorneys general, having failed to win in court and in litigation, have decided to revisit this in the court of public opinion, and in the court of public opinion, they have been much more successful.”

Why should the public support Craigslist?  Because of the principle that internet services companies cannot be made responsible for the speech of their users.  I think that we all agree that Google, Yahoo and Microsoft should not be held accountable for criminal content sent by private users of their email services.  What complicates the matter is that web services are varied.  Craigslist should not, for example, be allowed to create a category that is limited to illegal services (such as murder for hire).  However, most of what gets posted in adult services is legal, and illegal ads are posted in other sections.  In fact, legal precedent here concerned ads for housing.  In Chicago Lawyers' Committee For Civil Rights Under Law v. Craigslist the judge wrote:

Using the remarkably candid postings on Craigslist, the Lawyers' Committee can identify many targets to investigate. It can dispatch testers and collect damages from any landlord or owner who engages in discrimination. .... It can assemble a list of names to send to the Attorney General for prosecution. But ... it cannot sue the messenger just because the message reveals a third-party's plan to engage in unlawful discrimination

(quoted from WebProNews, which has links to the original).

Clearly, people are using the adult services section of Craigslist to commit crimes.  Those criminals should be stopped.  In my opinion, the attorneys general should do their job by using the list as a tool to investigate rather than trying to force Craigslist, and, by extension, all internet service providers, into the role of censor.