When we stand in front of someone and speak to that privileged individual “in real life,” we are generally aware of our environment.
We can easily asses that our communication is confidential because we can autonomously choose to speak when unprivileged people are not physically around to listen in.
We know that our communication has perfect integrity because we are physically present, observing and assuring that the speech is not getting messed with.
We also know that our communication is authentic because we are physically near the intended individual actively verifying them.
The foundation to communications confidentiality, integrity, and authenticity is trust, and the only way that we can assure technology-driven communication is trustworthy is with encryption.
Encryption is the technological requirement to assuring the foundation of trust that we fundamentally lose when people cannot be physically near.