Mxsmanic wrote:
As soon as the host of a discussion forum exerts any editorial control
over the content, he becomes jointly responsible for that content, and
can be sued over a post, a deletion of a post, or allowing a post to
stand, just like the author of the post.

That statement contains assertions that are wrong, at least in regards to
U.S. law, as indicated in this article:

"Good news for discussion list moderators: The Ninth Circuit has held that
under 47 U.S.C. sec. 230, discussion group moderators are immune from
defamation liability for messages posted to their groups, if those messages
were originally written by other people (whether group members or not) and
then sent to the moderator to be forwarded to the group. This is true even
if the moderators manually let those messages go through, or even if they
manually posted them; and it's true even if the moderators are quite
selective in deciding which messages to post. Under traditional defamation
law, the moderators would be legally liable; but 47 U.S.C. sec. 230 limits
online defamation liability in certain circumstances, and the Ninth Circuit
held that this is one of those circumstances."

Quoted from:
http://www.efl-law.com/internet-libel.php