I partly disagree with your comment (HN isn't an academy) but you make a good point that 4 downvotes are enough to effectively make a comment disappear. That can be abused to easily wreck good comments, adn genuinely shitty comments don't get enough negative feedback.

When you add in flagging and other factors, the 'mysterious black box + benevolent moderator' approach satisfies nobody and is easily gamed by bad actors. It's just an attempt at community security through obscurity, and like all STO approaches it doesn't work. There's also evidence to suggest that flamewars do a better job of eliminating toxicity over the long term than the approach outlined above.