Skyring said:
Another factor is the ease of access to the same audience. If a newspaper libels you, it is difficult to present counter-claims to everyone who read the original libel. But on Usenet, and arguably on Wikipedia, you have the same access to the same audience.
This argument hasn't featured as a serious legal argument in any internet cases that I'm aware of. The damage is done by the original defamation; the plaintiff's attempts to control the damage (which are notoriously counter-productive even where the damaged party is utterly above reproof) do not make the original damage any less serious.