From the 221 unanswered questions's comments thread:
One thing to keep in mind in this context is that there is some automatic deletion of old unanswered questions without upvotes. – Hendrik Vogt yesterday
@Hendrik: As we've got a policy of not down-voting, it's going to take a long time for anything to disappear that way! – Joseph Wright♦ yesterday
@Joseph: True, I just wanted to point this out to people who don't know that feature. – Hendrik Vogt yesterday
@Joseph: One way could be to do give the really bad questions a downvote when they're old enough; then the auto-delete mechanism has a chance. Or would that be too much against our policy? – Hendrik Vogt yesterday
@Joseph: we have a policy of not down-voting? – Willie Wong 18 hours ago
@Willie: Around the time the site started, there was some discussion about downvoting. The conclusion was that in the main negative vote numbers were offputting. So the suggestion was that voting should be a broadly positive step. – Joseph Wright♦ 17 hours ago
Should we revisit this policy, if it is a policy? See Inadvertently driving off new users for some prior discussion.