For what it's worth, I edit logs only under two scenarios:

1. If  copyrighted material  has been posted  without permission  and not
   editing the  logs could put the  host at fault (by  allowing continued
   retrieval of this information). This is  a case where lawyers call you
   unless  you  do something  and  where  not cooperating  means  helping
   software pirates who WILL use your site to download the software.

2. If messages were posted that create a major technical inconvenience to
   the users  of the service. Typically  this means someone who  posted a
   huge message, or cleaning up after a  mailing loop that made it to the
   archives (not that I've seen any of it recently).

I  never edit  logs  because someone  slept over  something  he said  and
decided it was best  to take it back, or even  because someone didn't pay
attention  when replying  and said  something embarrassing  in public.  I
think this  would convey the  wrong message -  "there's no need  to think
before you post,  you can always waste someone's time  later to take back
what you said". It also leads to a  big mess as I have witnessed a number
of times on  BBS systems where people can edit  or delete their postings.
Some  people did  get the  "offensive" message  and start  discussing it.
People who  logged on afterwards have  no idea what all  these people are
talking about and  ask what is going  on. The people who  got the message
have no idea what THESE people are talking about, since the author seldom
says he  deleted his message  from the archive.  In the end  people start
asking each other for a copy of the evil message, others suggest that the
issue should  be put to  rest since the author  wanted it deleted,  and a
very interesting discussion  about freedom of speech  begins where people
point out that  just because Joe wanted to withdrawn  his posting doesn't
mean the entire topic has to be  closed or the issues he raised shouldn't
continue to  be discussed.  It looks  very much like  what happened  to a
mailing list after a spam, back when spam was still new.

  Eric