Didn't someone(in europe) recently take the Catholic church to court as they wouldn't unbaptise them? (Without them needing to do something worthy of excomunication)
The point there was that he thought he had a human right to leave a "club" or "organisation".
Its easy to change your contact preferences to recieve nothing, then just forget about the site. Technically anything you post is public domain here and FF can do with it as they wish after your gone.
Just a thought but I guess under Data Protection the subject (user) could legitimatley request the removal of their details from the site. What about a web form that users who are really sure they dont want to be here can fill in. Staff then add them to banned users, change their username to "Deleted Member" and remove their email address?
Posts stay, user doesnt. Solves both problems?