This is probably the worst piece of policy on whole HN. It has a evil feel to it. If HN wasn't so interesting/valueable, this would be the single reason NOT to use it at all.
The alternative is what you see on reddit. A lot of threads from the past have posts deleted or overwritten with some script. You now have to dig through archive sites to find the comments, and you usually do find them.
I participate in Signal chats with self-destructing messages, too. But I post different things here and on Signal, under different usernames. Heck, after a few weeks I'll make another account here, anyway.
Even if you somehow deanonymize me, it's a risk I willingly took when I started posting.
Finally, if you go after HN for deleting comments, will you go after the many archive sites?