As a principle of communication. Working on a git repo is working on a shared artifact that's external to you and other developers. Retroactively deleting a message you sent me is literally like reaching out into my inbox and yanking out something that's mine now. Feels a bit different.
Yes. Very principled. I'm telling you that in practice, for the multiple large teams I've been a part of that have switched to slack, violating that principle doesn't prove to lead to problems. The benefits dominate the theoretical, academic concern. Try it!
In my company we use Skype for group chat (inb4 thanks for condolences). It has the edit/delete feature which I myself use mostly for fixing typos. But sometimes I'm a minute late to a discussion and see some deleted messages that are crucial to understanding what it was about. It's mildly annoying, and I was trying to reverse Skype to get at the deleted messages. It turns out Skype does store edits in its SQLite database, but sadly blanks out the original too if edit was a deletion. I'm too lazy to be bothered to set up a monitoring service that would make a separate, append-only log.
