Ages ago on This Week in Tech, Leo Laporte and perennial guest John C. Dvorak discussed the notion (in the context of Yahoo Groups at the time) that nearly every hosted content platform starts default-open to maximize the size of their user base but eventually passes over the "horse porn event horizon." Sooner or later, a critical mass of users with specific predilections would find the forum and use it for communicating on their, uh, topic of choice. And the owner at that point had two options:

- Do nothing and let the forum stay as open as it had been

- Ever be ad-supported or supported via mainstream sponsorship or partnership, or be purchased by a bigger company

... Few hosts choose the first option.