This is addressed in the upcoming Lemmy release 0.19.4 where contents will no longer be included in API responses. Until then it's up to clients to actually hide it. Content is kept for a few days to allow you to undo deletion, but you can also edit your content before deleting it to remove that. There is also a scheduled task running once a week I believe that will replace contents of deleted comments with something like PERMANENTLY DELETED.

Regardless, as Lemmy is a public platform, you should be aware that people may be storing this information on linked platforms regardless and may not respect the edits/deletions at all.

Just FYI, coming from a Thunder dev, the full contents of deleted and removed contents are available via the API, and it's up to us to hide the contents. It's easy to miss use cases (like another user mentioned you can see deleted comments by replying in Sync; that's just an (easy) oversight by the dev). I'm glad to hear that they won't even be available in the API starting with 0.19.4!!

If a post is marked as deleted, it's only visible to you. You can undelete it if you want to.

When your account is deleted, it is removed permanently (as permanently as it can be when federation is involved).

Others don't see the text of the comment though, it just says comment is deleted.

To answer your question, basically for Federation reasons (if I had to guess).

Its the same way with when you block someone, you're not blocking them from the seeing you, you're blocking yourself from seeing them. They can still respond to your comments and you wouldn't know they had.

~Anti~ ~Commercial-AI~ ~license~ ~(CC~ ~BY-NC-SA~ ~4.0)~