Why do people want to delete their accounts exactly? I have seen many asking for it after the server got hacked but i dont see how that would help them in any way?? Just change your pass and thats it or delete pms you dont want to be seen other than that, whats the deal with that?
Wipe their history. Some wipe because of privacy issue, some for starting fresh after a bad incident or something etc... If you do it manually, you will have to delete each and every posts which is time consuming. A simple button will be easier.
A delete all posts button might be an idea, but someone could accidentally delete all his posts, so perhaps a restore all posts button (that only works for a month) might also be an idea.
I agree that deleting posts gets complicated when having to take account of scammers covering their tracks, etc. It might be simpler to leave things as they are and let them manually delete each post one at a time. I doubt many legendary members with thousands of posts would want to delete them all.