Facebook is not clearly a public forum. My close friends do not constitute the public, yet CA got access to data that only those close friends would have otherwise seen.
Many aspects of Facebook with different expectations of private/publicness. Examples: comment form on public website powered by FB, FB page for å product, public FB group, private FB group, FB direct messages, FB group messages, personal FB wall/feed.
In light of these, categorical statements about all of Facebook is not very meaningful.
Facebook is not clearly a public forum. My close friends do not constitute the public, yet CA got access to data that only those close friends would have otherwise seen.