So at that point, you are basically saying "assume all communications over any medium is public", because this would apply to every form of communication.

That and most users aren't auditing each new version of the apps to make sure they're still doing what they say they're doing to protect data.

Modern secure messaging systems are typically OTR and have deniability: after the session ends, anybody can forge messages to make it look like they came from you. Sure the messages can become public, but they're no more "proof" than someone saying "X said Y".