Upvoting is useful to bring topics to the attention of people who may have missed a news story or hot new issue. But I don't think downvoting is a useful substitute for real discussion or debate. People shouldn't just click a down arrow if they disagree. Instead, state your case in a reply. A reasoned discussion renders moot a downvoting mechanism. Be afraid when a reasonable, civilized reply is pigeonholed or Spez-ed.