Lot's of interesting perspectives here. There is a lot to think about in this question.
A problem I note is the ability and inability to edit/delete posts. This would be a technical thing and it is already set up, but is there a need to change it to fit with whatever ground rules might be brought into exhistance?
On the one hand, a person may wish the option of removing their post, for a number of ligitimate reasons, (man I wish I could spell) and that ability to- delete- is a good thing to make available for them. This is only if the person is registered.
A guest cannot removed/delete their own posts (and may not be aware of that fact until later). They may not realize that there could be valid reasons for wanting to delete posts in future. This is simply a comprehension problem and the information about it is available, if one looks for it, but a guest may not initially do that. Their loss, I guess.
Also, registered people can delete their posts, if they so choose, and may do so for valid and sometimes, let's say- questionable reasons. When a guest communicates with a reg. member and that communication gets---uncomfortable, for lack of a better word, the reg. member can remove their posts from the thread, and leave the thread looking quite odd---with the guest responding to stuff that was once there but is now not. This will be confusing for new people joining the board, to say the least.
On the other, other hand, removing posts allows for the more "real" life experience of communicating, where sometimes people will say: "I didn't say that". Because those posts are now removed, there is the same real life reality of ---lying (not that a person couldn't lie their heart out if they wanted to to begin with). People do this type of thing all the time, so having the option makes the board--a bit more like the real world.
There is a lot to consider, if we bother to. Good for the brain cells, anyhow.
I guess trying to come to a perfect resolution, for laying ground rules on a board, such as this, is probably a bit of a dim idea, much like many things in life that are not so easily and clearly defined.