My bad, like Six Sigma above said, the guidelines do not include such rule. Since HN evolved /co-evolved with reddit and follows many of the conventions even more strictly, I thought this is also an HN rule. Intuitively, it also makes sense - 'upvoting', or irl aknowledging things you disagree with is how you would aknowledge that you see the opposing argument as valid, and will address the disagreement in a response. As opposed to downvoting, or irl ignoring, comments that fall so far out of scope of civil debate and are not constructive.
