This kind of thing can never be materially accomplished though. Whenever you post something publicly to the internet, any recipient can back it up indefinitely,

This kind of thing can never be materially accomplished though. Whenever you post something publicly to the internet, any recipient can back it up indefinitely, separately from the origin network. This is a fundamental material reality. No amount of legislation or centralized control of the content can overcome it. Ultimately people will have to culturally/collectively get over everyone's internet past, change their own behavior after understanding this new reality, and deal with the consequences of their speech. Even if it were possible, having the ability to remove all copies of past speech would probably produce worse social outcomes. I think I'd rather deal with a person's complicated history, than a history that has been selectively revised to deceive me. Private, perishable communication is only possible peer-to-peer, through a secure tunnel or network you own, with a person you trust to delete it. The same applies to verbal speech honestly, if you tell somebody something in confidence, it's up to them not to tell anybody else. People just need to accept that using twitter is like making a press release and not like talking to some friends.