The person who downvoted has to look out for themselves though. They may earnestly want to explain their choice so you can engage with their counter-points, but other observers on HN are extremely discourteous. Signaling disagreement usually just causes a flood of tribalistic downvotes or upvotes for in-group voting, as well as people disingenuously using the flag option, and spamming rebuttals, especially disingenuous calls for data or evidence or “citation needed” requests that aren’t actually in the spirit on engagement, just serve to DDoS real disagreement out of the conversation.

A silent downvote lets you avoid a lot of that, even if you respect the premise of the original post you downvoted.