The issue of whether to moderate or not is a thorny one for listowners.
I am a list owner with very little time (and, hence, an unmoderated list),
so this question is crucial also to me.
Junk mail notwithstanding, the fact is that there is a very fine line between
moderation and censorship, probably no line at all. In my opinion, moderation
is, as one correspondent here pointed out, distasteful.  I also think that it
is hard to justify.
Yet, cluttered lists are a nuisance.  What to do?  I have a couple of
suggestions:
      1.  Regularly send out to everyone a LIST POLICY STATEMENT and LIST
          ETIQUETTE.  It seems to me that each list should have its own
          set of rules of etiquette, and that these should be decided upon
          by the membership (not the list owner) and then adhered to.  I
          think it helps if all new signons receive the List policy statement
          and etiquette automatically at signon (as well as, or instead of,
          the usual "virtually yours" blurb that goes out.
          It is important that members both old and new know exactly what the
          list is supposed to focus on. It's amazing how many lists simply
          depend on their cryptic names to impart this information to their
          members. This list, for example, has a very general name that could
          accomodate postings on almost any subject.  On my own list, which is
          for teachers of English to foreigners (TESL-L), the membership was
          invited to participate in drawing up an etiquette or guidelines
          statement.  This statement now goes out to all new signons and
          regularly to "old" members too.  Among other things, it states what
          the focus of the list is, and mentions some topics that are
          NOT what we are about (linguistics, for example, and cross-cultural
          communications) and gives the names of other lists that DO focus on
          those issues.
          We now have a very clean, lean list, even though it is also
          extremely active.
 
      2.  Create "sub"-lists for those members of your list who have special
          interests and who want to carry on "conversations" on those topics.
 
Censorship is NEVER the answer to any problem, and it is a terrible precedent
to set. Those of us who are involved and interested in computer-mediated
communications should never lose sight of the potential for abuse.
Anthea Tillyer