Facebook interactions, like face-to-face interactions, are highly influenced by by expectations of agreement. What gets shared is what people think others will agree with.
Previous ‘spiral of silence’ findings as to people’s willingness to speak up in various settings also apply to social media users. Those who use Facebook were more willing to share their views if they thought their followers agreed with them. If a person felt that people in their Facebook network agreed with their opinion about the Snowden-NSA issue, they were about twice as likely to join a discussion on Facebook about this issue.