If a website can curate what is said so that it is visibly filled with defamatory material about a specific target, the organization curating the material maintains complete immunity from what would otherwise destroy a newspaper or any other organization that is actually liable for what is printed in it.
I don't think this should be possible for any organization, regardless of who they are. This immunity should require an extreme impartiality on behalf of the website. It's meant to protect organizations from speech they don't control -- when they assert any control over that speech, it's now their speech.