A lot of online discussion might be a lot more pleasant if people considered the perspective of themselves, or people they care about, reading their comments years in the future.
For sites like stackoverflow the intend is clearly to leave a lasting record of information, perhaps even more than answering the original persons question.
Or maybe that hasn't worked so well because it's not a sane default nor the one we operate in when we converse with others on a site like Reddit. For example, I'd like to see the argument for why my utterances on a site like Reddit need to be online forever and why I should want them to be. I can see why that's good for Reddit, but not why I should care.
HN doesn't let you delete comments. Yet nobody can even respond to my comments in the future. So it's a feature that does nothing for me no matter how great my comments might be.
What I'm not saying is that you should expect privacy for comments you post online.
The main reason I hate it when people send me voice messages is not that they're annoying to listen to, it's that I can't find them using the search function.
I'd gladly carry a recorder on me that would capture and transcribe all of my IRL conversations, but unfortunately many people would probably consider that creepy so I can't do that.
Something Gen Z gets right is preferring to localize their friend group discussions in more ephemeral places like Discord.
HNers get mad that they can't google "best blender 2023 site:discord" but who cares. IMO it was an accident in the first place that all of our utterances online are broadcast to everyone for eternity when we're almost always only talking to a handful of people, and only for the moment.