3rd Party Doctrine Should Go
Anyway, I think the problem is the "3rd party doctrine." It basically says you lose your privacy interest in anything you give to someone else. It is so grossly out of date and stupid, only a douche like Orrin Kerr could defend it. It comes from a 1976 supreme court case - US v. Miller.
In US v. Miller, the defendant was charged with a bunch of federal crimes. The feds had subpoenaed the defendant's bank for evidence, and got a lot of really damning evidence. The court of appeals suppressed this evidence because the feds hadn't gotten a warrant, and the standard for a subpoena is much lower than a warrant.
The policy, for decades, had been that information was protected only if the defendant "had a reasonable expectation of privacy that is generally recognized by society." This is a circular definition - because I know the feds can get my email, I don't expect it is private; if society feels the same way, then society doesn't recognize expectation of privacy towards email, never mind it is the feds who created that belief.
In a really misguided decision, the Supreme Court reversed the court of appeals. They announced a new doctrine known as the "3rd party doctrine." The opinion held that no one could have a reasonable expectation of privacy toward any information "voluntarily" given to a third party. They skipped the question of confidentiality, though have since held people can have a reasonable expectation to privacy when confiding in doctors, attorneys, and under a few other relationships.
In US v. Miller, the banking relationship wasn't considered protected, and the bank was required to keep the records under the "Banking Secrecy Act," which is like a two-step to getting anything you want: require it be kept by a 3rd party, then use the 3rd party doctrine to get it. Of course NSLs are easier.
When the 4th amendment was written, it focused on privacy within the home because that's where everything private occurred - private conversations, letter writing/reading, bookkeeping, etc. Now that we do these kinds of things outside the home, and the 3rd party doctrine says we don't have an expectation of privacy in these things.
With stuff like remote storage, except where covered by the gutless Stored Communications Act (part of ECPA), the justice department has said 3rd party doctrine applies - e.g. online backups, email archives, stored voicemail, etc. The 3rd party doctrine is the problem.
The other problem, IMO, is that privacy case law is always decided with some guilty criminal on the line. Some evidence shows they're guilty as sin, and they try to get the evidence suppressed for privacy reasons. Courts are loathe to let the obviously guilty go free, so they create privacy precedent that affects us all, only by looking at criminals.
The 3rd party doctrine just doesn't work in today's environment. With NSLs, CALEA, FISA and FISC, federal law enforcment has too much in the way of tools already.