That solution makes no more sense than holding the U.S. Post Office liable for anonymous letters. The publisher of a newspaper can reasonably be expected to know what is appearing in his pages. But an ISP has no practical way to monitor the enormous flow of information that passes through its servers–and if it could, we wouldn't want it to. We can–in the context of copyright infringement we do–set up procedures under which an ISP can be required to take down webbed material. But that does no good against a Usenet post, mass email, webbed defamation hosted in places reluctant to enforce U.S. law, or defamers willing to go to the trouble of hosting their web pages on multiple servers, shifting from one to another as necessary. Defamation law is of very limited use for preventing online defamation.