This reminds me of the way I hear they do state censorship in China. The censoring agencies don't actually give out any specific guidelines on what is allowed and what isn't, instead just clamping down on cases they do consider to be over the line. As a consequence, everyone self-censors more than they might with specific guidelines: with the guidelines, you could always try to twist their letter to violate their spirit. Instead, people are constantly unsure of just exactly what will get you in trouble, so they err on the side of caution.

While I strongly oppose state censorship, I can't help but admire the genius in the system.