I'm thinking strict moderation goes hand in hand with size of the population; in low population environments, little to no moderation is sufficient. The people govern their own culture, and with sufficiently low immigration rates, they can adequately teach newcomers the culture.

But as the population increases, driveby-posting becomes the norm rather than the outlier, and large swathes of newcomers can join at once, the culture cannot be taught at a rapid enough pace to survive. It either degrades, or enforces itself by means of an iron fist.

My thinking essentially stems from eternal september. Wikipedia's early success did not require heavy moderation, but once it became the predominant wiki, it's survival, I think, neccitated it.

The details may have issues, but the overarching idea, defending the culture from the unwashed masses, might still be correct.