From CrazyThingsThatMightSaveWiki
A lot of people have this bloodthirsty urge to kill kill kill, preserving only their favorite part of the wiki (be it PortlandPatternRepository, programming, programming related, whatever). This will not resolve the current social problems of the wiki for two reasons.
1. OffTopic pages aren't the problem. The off-topic issue is blown out of proportion, honestly. Just looking at QuickChanges this day of 2004-08-03, all pages are on topic. (Lest someone claims that RichardKuliszFanClub is off topic :) We might need to look elsewhere.
Furthermore, it wasn't the off-topic issue (in general) that prompted this discussion. It was the "certain assholes are scripting 'bots to a) enforce their will on or b) spitefully damage Wiki" issue. Off-topic-ness is a tangential issue (the current EditWar sprang from attempts to delete, and prevent the deletion of, WikiBlackList - an obviously off-topic page); but if off-topic pages were the only problem, we wouldn't be here wringing our hands quite as much.
2. We've come much too far to delete all off-topic pages. While deleting noise is good if the act is unopposed - when the deletion of noise causes the noise to be amplified (due to an Edit War arising when one person's noise is another person's signal), the deletion of noise has then become counter-productive. Any attempt at mass deletion will automatically trigger a mass restore. As shown in this testimonial:
Fat chance. The one time I attempted that, many months ago, the same guy who has recently been losing his temper lost it on that issue, too, and did a restore war (I backed out rapidly but others deleted for a while). A single determined person can (and, as has been demonstrated, will) ensure that OffTopic pages remain. So your suggestion is already proven to fail, at least over the short and medium term.
Also, he's not alone. Every attempt to enforce a stay-on-topic policy on older pages brings people out of the woodwork to protest. There is no consensus.