It's also important to recognize that "the reasonable expectation of privacy" can refer not only to expectations about the effect of physical barriers to legal

It's also important to recognize that "the reasonable expectation of privacy" can refer not only to expectations about the effect of physical barriers to legal intrusion (e.g. curtains), but reasonable expectations about what is systemically necessary for a democracy to survive. Democracy is not magic, and it can be easily broken. The reasonable expectation that the people who are sworn to protect and uphold it won't actively undermine the system means I can reasonably expect privacy in a wide variety of situations where it's technically possible to eliminate it. After all, we don't "limit" the houses that the police can search to those they can physically invade. In reality, they have the material capacity to walk into nearly any space they like. Indeed, this is why we have an additional layer of laws to constrain them, as physical barriers obviously aren't enough. In other words, saying "You have no reasonable expectation that third parties won't freely share everything they know about you with the police because technology" is as stupid as it is dangerous. It is also demonstrably wrong. And when it comes to public officials sworn to uphold constitutionally protected liberties, it is reasonable to expect that they will adhere to both the letter and the spirit of the law because that's what the continued existence of a democratic republic depends on. The truly unreasonable thing is believing this isn't the case.