slightly unrelated note but you both are also talking about the way the official Snapchat app chooses to handle snaps (opt in and notifying the user) when theres a multitude of workarounds and non-official snap apps only a google away that make it extremely simple to save a picture someone sent to you without the sender knowing.

Preventing phone-screen capture isn't really something you can't get around but Snapchat could certainly afford to put their money where the mouth is and try to provide their users with a safer experience by cracking down on 3rd party apps.