If something dubious is posted to the front page for example, it can be quickly removed (e.g. voted out of existance). Notice that OT stuff is still allowed -- just discouraged in general unless the "community" thinks it's worthy.
I don't agree with this, it's too much "let the market decide"
in economic terms. Your suggestion would mean that if I rally
enough people interested in collecting miniature kobolds to
come here, we could discuss collecting miniature kobolds on
perlmonks, and even vote off any Perl related articles from
the front page.