He can actually delete a thread created by himself but like you said the Scrapers we have can simply make one have access to almost everything posted on the account even after they got deleted.
He actually can not delete his threads.
He only can delete his threads if he is a forum moderator but he is not.
He only can edit opening posts of his threads, delete all words, change the title and lock those threads or move them to Archival. It is not thread deletion by the way.