In particular, if you decide that a comment you made was overly negative, or offensive or has some other issue, then it is good for the quality of discussion that you be able to take the action and remove it. You are allowed to do this for a short time period after creating it, I think you should permanently be allowed to delete it.
I know HN does not like comments to be deleted because it breaks the historical value, but I think people, privacy, quality of discussion and individual personal right to curate your own online presence are more important than HN's right to maintain historical integrity. HN doesn't see it that way as far as I understand but hey, it's their site. Don't like it, don't comment.