It's better to have the functionality with the notification that it might not be respected/work than not have it.
Discussion
It’s weird because you presumably only use relays you trust somewhat so you should be able to delete. But on fedi DMs aren’t even encrypted so admins can see your posts and images but nobody seems to care about that.
Well the issue is anyone can submit your notes to any relays they want, so if someone was autistic enough they could just make a bot which automatically submitted your notes to a relay which didn't respect deletes. Or they could just save the notes and submit them once they are deleted.
Anyone can rebroadcast any note to any relay. Since a note which is valid is complete as is and there is no need of resigning or whatever to reboradcast. If you bitcoin, then think of a singed note like of a signed transaction.