Earlier quoted context omitted.
If I was well-assured that if I participated in Facebook all of my posts, private messages, likes, etc. were truly private and would never ever be released to the gov't or any other entity in any way, ever, under no condition such that they could prove to be self-incriminating, I would use Facebook. But I know that isn't the case, and hasn't been the case for a long time, and thus I don't use Facebook nor have I ever…
Is something you share with hundreds of people "private" whether or not the government can see it?
I think a public post is public, so it's fair game as concerns the gov't trying to use it in whatever way they wish.
On a tangentially related note: you have said much about what constitutes an 'unreasonable' search as the founders may have meant it: that, e.g., one's personal e-mail contents, private Facebook posts, etc. are not as "personal" as one's personal belongings in a home (like a diary). I had a diary when I was young (teenage years), in it I wrote fairly personal things. I guarded it with all my might, and I think I was successful: I don't think anyone in my family ever even knew about the diary's existence. But yet I did not write things highly highly personal, because I was acutely aware that it was just a physical grab away from anyone. When I started using the Internet circa 2001 I finally felt and experienced a liberty that I never had had before. If you had access to my google searches you would have insight to my most personal being: what kind of porn I liked, my trying to find out ways to commit suicide (teenange angst phase), and so on -- things that I would never write in my diary. That is, I felt more confident about my privacy on the Internet than I did about a personal belonging in my own house. Now, that might have been the result of being afraid of a religious helicoptering mother and so not everyone's like me in this regard... but don't you think the founders would rather empathize with my situation and see things my way than yours? That one's Internet belongings should just be as personal as one's belongings at his home?