It’s true of any contentious content. The commenters who engage are usually the ones who want to push back against the main article (otherwise you just get a highly upvoted post with minimal comments because it’s hard to come up with a value-adding way to say “yes, this”). But you end up getting different people commenting on both sides, with neither half as invested when the source agrees with them. Grouping them together as a cohesive “HN” obscures that division, and makes it seem like the position suddenly reverses.