I have never been able to accidentally broadcast my impolite opinions on the lukewarm breakfast burritos to everyone in my company in a casual conversation.

The vast majority of memories about conversations are partially or entirely ephemeral, and they aren’t recorded.

In real life it's pretty hard to accidentally say your private keys or 16-character alphanumeric password to people.

On the other hand, maybe it's best they can't be deleted, since that will force people to rotate them.

If you accidentally post a key/password in public/semi-public place you should immediately rotate it, regardless of whether or not you can delete it.

Yeah, but there's also defence in depth, right? Being unable to delete a message means you're exposed to anyone who can see your main Slack channel for the stretch of time between posting and rotating, as opposed to the smaller number of people who saw the message or who are running a weird patched Slack client.

This isn’t defence in depth, this is security by obscurity.

Also, honestly, if you are manually typing passwords and copy/pasting private keys, you can’t expect any security anyway.

It's infinitely less likely that you tell someone something and realize they are the wrong person though.

Can you recite, verbatim, every casual conversation you'd had in the past week? What about the past day?

Not everything is meant to be permanently recorded.

There is no clipboard feature in casual conversation. And many other $differences.

No mulligans? I don't think I want to talk with you!