I disagree with the author.
I see no point in making my conversations accessable for everyone, especially if they cant actively participate in them.
There is no need in grouping your friends in any way, just create a circle with all your friends and those will behave the same way facebook does,at least if I got it right (by the time I got my invite it was already full).
I think there is a difference in what I want my friends and family to know about me and what people I just know but have no deeper relationship with should know.
Posting something publicly would make it accessible for everyone, twitterlike.