I think we see enough support request on the subject that it would be a good idea, this way we have something to reference to when people ask how they make their whole journal secure.
It could read: "You can make your existing journal "friends only"/"private" by going back and manually changing the entries." or something. Perhaps someone better than words than I would word it better. *lol*
A little birdy told me there was some talk about changing the way journals change security settings...so if this is true, I'd like to suggest my idea as an interim change.