Maybe we just have a very different threat model?

Snapchat style messages completely solves:

- someone you trust now later becomes untrustworthy and would use old messages against you

- messages are stored on your phone and can be found by someone else later

neither of these can happen if deleting messages is not an expected and normal part of the protocol

it does not solve the problem of sending messages to someone who already wants to hurt you (ie. the public internet)