This demonstrates a fundamental misunderstanding of digital privacy. You can never be guaranteed that data is deleted, just like you can never be guaranteed that someone has "forgotten" something. It doesn't matter what any entity claims they are doing under the hood, you have to assume they can't be trusted. That's not an expectation you can have, and not something privacy advocates are asking for.

I'm posting this comment publicly, and there's nothing stopping any random user (or non-user) from scraping this lemmy instance and archiving the data themselves. I know that when I post it. Same for reddit, raddle, any mastodon instance, etc. I can copy the text and usernames of everyone involved in that raddle thread and do whatever I want with it, there's nothing anyone can do to stop me.

To think otherwise reminds me of that first day on the internet kid meme. "I deleted my comments, hah, they'll never get them now!"

What I can demand is: if I send a message directly to another party, I want to be able to verify that that party and ONLY that party can read the message (end-to-end encryption). I can also demand that they not require me to dox myself to them, that they not run weird js-based fingerprinting/port scanning processes on my system/network, and that I am allowed to connect to their services through a VPN should I so choose.