One of the tenets of social media is sharing. You post something for people to see. You are not entirely sure who might see the post, but whoever is interested can visit your page and see the post. While visitors are on your page, they can comment on the post. They might even decide to share the post with their friends, if they find it interesting enough. That's what makes social media really powerful. Without visitors commenting and sharing the post, Joseph Kony becoming public enemy #1 in matter of a week would not have been possible.
If you don't want to share things with public, there is one-to-one communication channels. Email, IM, group chat, internal collaboration tool like Jive and Yammer can be used to share messages with a limited set of recipients. You know exactly who are receiving the message that you are sending, and their is tacit social contract between sender and recipient(s) that the message is intended for people included in To and CC list.
If you don't want to share things with public, there is one-to-one communication channels. Email, IM, group chat, internal collaboration tool like Jive and Yammer can be used to share messages with a limited set of recipients. You know exactly who are receiving the message that you are sending, and their is tacit social contract between sender and recipient(s) that the message is intended for people included in To and CC list.
