Anyone can post, but not everyone posts well. Good contributors understand the topic of a message board and make sure that their posts are in line with that topic. In fact, excellent contributors not only understand the topic, they are fully in tune with the purpose and theme of the board. One of the jobs of a contributor is to make the board enjoyable to everyone who reads the messages. Good contributors never flame anyone, no matter what the temptation, and the best contributors go out of their way to show respect for other contributors, the moderator and anyone who might be reading the messages.
Message boards have a life of their own, like any other community of living, intelligent beings.
These people are very prolific, very knowledgeable and extremely respected. They do not spam the board with advertisements Bad contributors, on the other hand, do the opposite. Smart moderators support good contributors, as they understand that this is what makes a board not only survive but prosper. In fact, if a message board can get even one good contributor, it will soon have a large following of other contributors and readers. I have seen many message boards fail when one of the star contributors left the scene.