While reasonable people can disagree on this point, it seems a valid point of view that once you've publicly posted something that's part of an online conversation you can no longer unilaterally delete it.

But once you delete your account those posts can be attributed to “Deleted User”. HN doesn’t even do that.

This isn't a new thing. You couldn't typically delete a Usenet post either.

What has changed is how easily and casually people can put things out in public without editorial oversight that they may regret.

In the early days of Usenet posts were ephemeral and would only last a week. That expectation was baked into the culture and everyone was surprised to find a sneaky organisation had been archiving it all to monetise later.