If you are an owner of a forum, I bet that at one point you have faced a dilemma that a user asks that their account be deleted and all their posts deleted. So what have you done? Legally, they own the copyright on the material that they have posted but you must remember that they gave you permission to do whatever you like with that copyright. To other forum owners who are facing this dilemma, if they continue to demand that you remove all their posts, you must explain that a lot of discussions on the forum will be ruined. Nevertheless, there has been no court yet that has been asked to rule on a situation like this so it is not entirely clear what is likely to happen and if you ask the lawyers, they are divided on the situation.