OP here.
I've been participating in online communities for almost 20 years, from the most uncensored, chaotic free-for-alls to the most tightly-controlled moderated mailing lists. It's all too easy for a productive, collegial community to devolve into troll, snark, abuse, and spam, and drive away the most loyal long-time members, whose long-term perspective and institutional memory provide the core of the experience for new and old alike. Similarly, new visitors view the signal-to-noise ratio as so high that they won't bother to participate.
Having some core values established, a mission statement, so to speak, provides a baseline to which the community may refer when performing the kind of self-policing others have described above. Occasionally, in extreme cases, someone with administrative access may have to step in to clean up, but that's not really what I was referring to here.
I hesitated to post this, as I love the rather free-wheeling nature of GK, but over the past month or two I've seen a few posters without the same sense of community crowd out the long-time regulars and the new arrivals. Since no one seemed to be reeling them in, I thought that setting out a few simple sentences of guidance might be useful to help the community steer things back in a productive, fun direction.
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(As far as "censorship" is concerned, there were a specific few personally abusive posts and wildly-off-topic threads that I saw that were doing no one any good but the posters' egos. In many well-run communities these don't stick around long before being deleted, or are left standing as an example but locked to new posts.)