Defamation and archives

Unacceptable publications: falsifying the record?

One problem we are having to grapple with increasingly in the internet age is that of archives. In the past, if a book contained illegal or defamatory material, you would supress its further publication, but it took too much effort to engage in book-burning, and libraries would probably retain their copies. No-one would attempt to get back all copies of last week's newspaper, or to fillet the publisher's archive. In the internet age we have semi-permanent, searchable, global access to almost anything, so the damage done continues long after publication of even the most ephemeral comment. How far is it acceptable to require filleting of archives to remove illegal or defamatory material? When does falsifying the record become worse than dissemination of the unacceptable material?