First of all, I have no idea if you will understand my ramblings, they are mostly psuedo-sentences from a tired Swede who's spend the night learning OCaml. You can try at least...
Okay, here goes. I am currently an active member of well over a dozen forums ranging from computer forums to forums dedicated to headphones, private forums and forums dedicated only to video game music, I even moderate one of these forums and does freelance administration jobs for three of them.
I have learned one thing from reading all these message boards, it's a simple truth, you can accept it if you wish, if you don't - then don't...
The golden rule of an internet message board is, that the harder you moderate, the closer the original theme of the webpage/forum (say role-playing games) you are going to get, the more mature these discussions will be.
Rule number two is, that the definition of moderating hard increases as more people sign up on the forums, which conclude that the category of valid OT posts decreases per member joined. You can still post OT threads, but the closer these threads are to a forbidden subject (say politics), the higher the population of the forum is, the higher probability the thread will be closed.
This is very simple, actually. In a forum with ten members, everyone will sooner or later know each other. There isn’t need for many rules at all. In a forum with thousands of members, where some might even have joined not to talk about the particular subject (say dungeons and dragons) but to "chat" because of the huge amount of nice people around (known as the Off Topic-forum problem), there are doomed to arise more problems, which leads to a more strict way of moderating things.
That's why there isn’t such thing as an Off-Topic area here. That's why the moderators close a thread they don't think is appropriate, that is a thread they believe will cause trouble in the near future. That's what moderation is all about, to keep things on a certain level.
And because of the strict moderation here, THAT'S why things are still very mature here. I promise you, that things would not be this nice if every single OT post was allowed.
So, to conclude: The larger the forum is, the worse impact OT threads will be/have, or more precisely - the larger the forum is, the better it is NOT to create an OT forum or allow lots of OT threads.
Anyhow, I hope you get the point. If you don't, I hope someone will quote this post and develop my thoughts even further.
