> So I don't think I actually have a problem with businesses handing over their customer data if there is a valid warrant or subpoena. That's the system working as intended.

I disagree -- the third party doctrine that allows for governments to avoid serving/addressing warrants to the people whose data is actually being subpoenaed directly leads to things like the FISA warrant-rubber-stamp courts in the US. If the data stored on third-party servers on behalf of someone is not considered "papers and effects" of that person then it is entirely justified to subpoena every email stored on mail.google.com because it's just morally equivalent to a subpoena for "all of Foomatic's business records between 2020-2025".

It seems bonkers to me that things that are essentially implementation details (such as the way that MTAs work and the lack of crypto-obfuscation in email) should allow for a legal interpretation of the 4th amendment that effectively neuters it. Letters sent via snail-mail are handled by several third parties in a very analogous way to emails but (mostly due to historical reasons, such as the fact that letters existed during the drafting of the bill of rights) we do not apply the third-party doctrine to letters.

Of course, the US government has spent decades chipping away at the privacy of snail mail, so eventually we may end up in a world where snail mail and email are treated the same way (just not in a good way).