How does this world view reconcile with the fact that many different states have 2 party consent? Or the fact that considerable money and effort have been spent on concepts like OTR?
People expect others to have some discretion in what private information they pass on to others. Most applications have this assumptions built in mind.
You can easily forward a single email to someone in gmail, but there is not 1-click solution to send all of your emails to someone else.
That’s actually wrong. Right now, today, you can write apps for the Gmail platform that could have this ability as soon as someone authorizes it [1]. So everyone is down on Facebook, who disabled this ability 4 years ago. What about Google?
This isn't your nana forwarding chain mail.
So perhaps it's not an expectation of privacy, but more of an expectation that your private messages won't be distributed by third parties for profit.
The world doesn't just give you privacy. If you want any, you have to work at least a little bit for it.