Once you share something on the internet, its potentially there forever. You can only make it more difficult to be found. If its controversial, the chance of it getting copied (e.g. screenshotted) is bigger. There's a name for it too: Streissand effect.

That's why Snapchat provides a false sense of security. On a rooted smartphone the privacy feature of self destruct does not work, and there's always the analog hole. There's extensions for platforms like Reddit which show supposedly moderated/deleted content.