When you share something, whether it's publicly or within a closed loop of social media, it is inherently not within your control anymore. You can NEVER create any kind of guarantee that clicking "delete" erases every potential copy of the data. Folks need to have that in the front of their mind when they create and share data on the internet. Full stop.

Now, morally, I could maybe understand where you're coming from. It's more of a "jerk move" than it is subverting a technical promise.

But I backup my Telegram messages occasionally through their data export tool. Are you proposing that I cross-reference my own backups with messages that get deleted from our chats? Same thing with WhatsApp.

Assuming I'm not commercially monetizing those backups, I consider it well within my rights to have a copy of conversations I've held with people in the past. And in fact, it may be by design that I don't want them to manipulate the "cloud copy" of our conversation in the future.