Add a "time-out" mechanism: If a comment is killed by the editors (and/or by being flagged many times) then for the next X minutes (I'd go with X=60) handle any GETs from that user by redirecting to a page saying:

  The following comment has been judged to be unhelpful
  and as a result you are now on time-out:
  <comment quoted here>
  You may return to Hacker News in Y minutes.