Guest posting has its good sides, but the worst side is:
SPAM Bots that can get past the CAPATCHA images. (Obscufated images)
Then, there are abusers, who post and post.
Then there are the people that dont understand that its not an email system, but truth be told, a lot of the registered users think of it that way.
But you get more posts, and more users involved, and more people with a
face
(but then again, the SPAM bots came with
's on their non-existent faces...)
Being as literal as possible:
The more users, the busier I keep myself...
It is such a PAIN to register to websites. You always have to worry about Spam, and about keeping track of it, and logging in. Some people just come here once, and then leave. You could not just enable it on one newly created board, since it would not be categorized. (And there is enough non categorized problems already. It could be a guest board, and then if it gets approved, it can be moved out.)
There are LOT of things to consider....