There should be an eMail Forum because it is an integral part of a web site. It is a complex subject and its discussion would be of inestimable benefit to many including myself. It is ludicrous that the primary method of internet communication should not be included in the web's foremost discussion forum.
The liability concerns (especially in a country as litigious as the USA) would certainly require pre-moderation with several moderators, perhaps with legal training. The actual and potential costs to WebmasterWorld unfortunately outweigh the benefits to community members. I wish it were otherwise but it isn't.
On the side issue of whether eMail is or is not a marketing tool/method/device: eMail is a method of communication (as are face to face speech, telephone, mail, radio, newspapers, etc.) and as such can be used to propulgate advertisements.
Not all communication is marketing but all marketing is communication.