Why not let a user delete his own posts/topics? 
is it possible?
Once a post is made, control is given to the community. Thus, other posters retain a sort of right-of-way on that post, and deleting it would violate that right. While a post or thread that you make is still ‘yours’ in that others have the obligation to credit you with the ideas and language used, your control over that thread is limited in the interests of the community.