One of the most intriguing things about YouTube is that it isn’t over-run by porn. I’ve often wondered why — after all, every other unmoderated publishing opportunity on the Net seems to have succumbed. This thoughtful piece in the NYT explains that YouTube’s founders shrewdly anticipated the danger and installed sophisticated filtering software that spots and refuses porn — with interesting effects.

By keeping obscenity in check, YouTube teems with video of near infinite variety, stuff that thrives when pornography, which is hard to contain once it takes root, has been banished. YouTube risked losing millions of viewers when it made rules against pornography. But it has gained radical variety, the kind that defines the most robust ecosystems. YouTube’s dizzying diversity, in fact, now makes online porn sites that purport to cater to a broad range of tastes look only obsessive and redundant…