Why so pesimisstic. In a sane world (and probably in the world where they want to say "just use WhatsApp, we're better!") they'll say "This user is using an unencrypted app. [Paragraph about how all your nudes and contents of bank account will be stolen]. Are you sure you want to send them a message?".

In a better world, something like https://otr.cypherpunks.ca could be implemented, where the user has control of their own e2e...