I think if you go to your post as if to edit it, it gives you the option to delete your post but not the thread. You might try to modify your first post and see if it gives you that choice.
I recently made the mistake of double posting and tried to eliminate the echo but the delete option never appeared. The best I could do was just eliminate the message body and replace it with 'duplicate post removed'.
I guess the moral to the story is, think very carefully before starting a controversial thread because once it's there, it's too late unless you do what Bob did. That only works if you modify it BEFORE there's any replies.