Should all comments be deleted?

Sometimes, mods delete comments. In fact, sometimes mods delete entire comment threads. This inspires people to come to this meta or site-specific metas to ask "why were my comments deleted" (e.g. here, here and here and many many others.) There is even a tag that seems to be specifically for this thing, deleted-comments.Although I would not go so far as to claim consensus on the matter, almost universally an answer is given and receives upvotes that hinges essentially on a line from the comment policy "Comments are temporary 'Post-It' notes...Read more