Information shared to a third party that the first party could no longer deem under its control, that is what is no longer considered secret.
This means that yes, the government has perfectly readable access to everything I post on Twitter. That's fine. This does not mean that they have access to the contents of my Livejournal posts that are not shared. While it is a factual assertion that I have shared them to a third party, another, better interpretation is that I have shared them to a contracted vendor with whom I expect privacy, even where I know that they may not be able to access it.
There is case law on physical proxies. If I am the renter of a storage locker or facility that has a lock on it (password), then I have a reasonable expectation of privacy there, even though the storage facility is clearly a third party. Because I have a contract with them, and in that contract, I do not grant wide-open access to my belongings, the storage locker is an extension of my papers and effects.
I get that you and we all have different interpretations of what we would expect privacy to mean. But the government only has the one that it has to go by, the law, and the law was made much more expansive by the USA PATRIOT act and only brought back in a little bit by the 2008 Amendments. I could have sworn that the Supreme Court has had a chance to strike down part of the USA PATRIOT Act by this time and hasn't.
I like your analogy on physical proxies, but I didn't need convincing that information given to a third-party on the Internet deserves a "reasonable expectation of privacy" (up to the limits of the privacy policy itself, though...). I just don't think the law agrees at this point, which is why I'm pushing back against people with the idea that everything the NSA has ever done is illegal.
The law needs fixed, once and for all. I think most of us agree at least in theory that there is a need to handle counter-terrorism and domestic law enforcement so we also need to decide what "features" (if any) are built-in for that.
And then we need to decide how far those laws extend to cover those from outside the U.S.
"But the government only has the one that it has to go by, the law"
Technically, the 'one thing' to go on is the Constitution. Any law that violates the Constitution, plainly read, is not a law at all. No citizen is obliged to abide it, no court is obliged to uphold it, and no agency is obliged to enforce it.
Obviously the world exists in far less black and white terms, but at least portions of "the law" that they are following have been deemed unconstitutional by the courts, which should cast a long shadow of suspicion on the rest of the provisions.
This is why we ought be thankful that Snowden spoke up. Too many people derive their morals from what is or isn't legal, and too many people would accept unconstitutional infringements to the constitution that makes them feel safer. To paraphrase Neil deGrasse Tyson, "I don't fault people for being willfully ignorant, as long as they know they're making a tradeoff for mental comfort - I don't want to be them, but I understand it whenever I can't fall asleep because I'm worrying about the state of things" -- what polls on this issue have shown is that far too many people just want to be governed kindly, which is either an indication of a dumb, complacent society that has lost its fierce American spirit, or is an indictment on all people unilaterally.
"A republic, if you can keep it," implied that there would be work involved. What we've shown over the past few decades is that, as a citizenry, we aren't willing to put that work in.
This means that yes, the government has perfectly readable access to everything I post on Twitter. That's fine. This does not mean that they have access to the contents of my Livejournal posts that are not shared. While it is a factual assertion that I have shared them to a third party, another, better interpretation is that I have shared them to a contracted vendor with whom I expect privacy, even where I know that they may not be able to access it.
There is case law on physical proxies. If I am the renter of a storage locker or facility that has a lock on it (password), then I have a reasonable expectation of privacy there, even though the storage facility is clearly a third party. Because I have a contract with them, and in that contract, I do not grant wide-open access to my belongings, the storage locker is an extension of my papers and effects.