Hacker News is about pseudonymous discussion. Only a small percent of HN posters are building a brand name. Twitter is much more real-name based and personal brand-building focussed.

Jumping in on a bandwagon to signal group membership in an in group can help brand-building. Going against the in group is potentially fatal to your brand. The risk/reward balance does not favor genuine discussion of a controversial topic.

On HN most comments are up/down voted based on their content. The post authorship usually matters little. There is little benefit for the author to announce support of a popular position and little risk for the author to express an unpopular one. So discussion here can be more about substance and less about signaling.