That's an interesting question; I suppose I may start threads that I wouldn't want "select" others to see and/or make a comment on but oh well, I just have to put 'em out there and hope for the best.
There use to be a message board that I belonged to where it was possible to block a specific member's posts from you seeing them. They could openly talk about you all they wanted to and you wouldn't ever know what they were saying because thier posts were blocked from your viewing.
As for me as an SP member being able to delete and/or block other members threads/posts, well heck, I've been wishing that for years now, LOL!!!!!