It depends I think if the moderators consider your request reasonable - if you start topics which people contribute to, then it's rather bad form to make all their effort vanish? I think they consider it if what you posted was litigious or dangerous - that kind of thing, but you set your profile to not allow us to even find most of your posts, and the ones that are there seem quite safe and not likely to come back and bite you. Normally with forums, when you join you just accept it's there for ever, and of course with wayback machine and others, people could still find the posts if they knew your old username, but that's pretty unlikely. If you want to leave just leave, personally, I'd rather forums don't remove people - some do it by removing the username and leaving the content, but I think the rules don't allow removal of posts unless there's a good reason, so you might have to make a decent case, because I don't believe it's an on-request thing!