I must agree with Dave A.
You can't share a link with someone who is not a member. Say I want to explain to a friend, how I built my little wind turbine. I give them a link and they would have to join to see it. When I made my diary, the hope was to help others, not just members.
I knew my diary would be viewed by the public when I did it.
There are other diaries that I personally feel should be in public view. Ghurd's controller comes to mind.
respectively, Kevin