I agree for catastrophic mistakes. It doesn't mean the feature is rendered useless for the non catastrophic ones.

Which one occurs more often than the other, that's another question, but I'd argue that the later is more common, and there is no doubt that people knew, in the event they wrote a very catastrophic secret, the limitations of the edition/deletion of messages (as long as most people nowadays seem to know about screenshots being a thing)

The issue is that zapzupnz deletions to propagate. This can only be ensured in locked-down systems.

There's a difference between offering corrections and retractions that others may or may not accept and actually enforcing deletions. This is both socially and information-theoretically true.

All I said is that the deletions should be propagated. The presentation of this can only be ensured in locked-down systems, but the actual propagation is simple enough. Just as the server can send all users within a channel "so-and-so said this message", it can say "so-and-so deleted this message" — it can be left up to the client whether to actually remove it or perhaps just hide it, ready to be shown again with a click.

Obviously on Discord, one is tied to the official client's behaviour since the ToS discourages third party clients. However, for Slack, Mattermost, Matrix etc. clients, the possibilities widen up.

Ah, I read "deletion" as the actual effect, not the request for the action to be performed.