It's like email: after you send it off your own MTA, you have no control over what happens to the copy at the far end, or any other MTAs it happens to traverse.
ActivityPub does distribute updates to posts, including delete intents, but instances are not bound to honor it. Same as how recalling an email isn't guaranteed to work.
Disturbing? I'd say more that it's sobering. I think it should prompt people to think more carefully about their accountability for what and how they post. I also may come to change this opinion over time.