Huh, well apparently one can, if one deletes their own post.
As far as I know, actually deleting a post requires admin access: if you delete your own post, it just removes your authorship notice and de-indexes it from the list of posts, but it's still available if you know the URL. E.g. Roko's ugh fields post is still around.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.