As nice as Ramit’s post is (and I do acknowledge, building a community is key), without the option to have a more limited author-level, even a single bad egg (or argument) can destroy a wiki. Mine never recovered from the contributor’s quarrel, as the people involved stopped participating. Now, that’s clearly a social issue - but the situation wouldn’t have gotten as out of hand if they had been unable to delete pages and revisions.

So it’s truly regrettable that PBwiki’s free wiki’s don’t include Contributor access levels to allow people to throw open the doors and invite anybody to come and participate — without risking their entire site.