My point is that proposed discussions about US policy that point to something that some HN user has decided is worthy of praise never seem to get traction here, while discussions that are objectively critical of the US seem to proliferate (with no substantive discussion in opposition in the comments section).
That's the real issue. Humans do not engage in productive discussion if everyone holds the same opinions. Find me a set of conservative opinions that has resulted in substantive engagement here and I'll be happy to update my priors. Until then, what I see in the political threads here is an echo chamber, with the (conservative) opposition either downvoted or reluctant to post. I can't tell you why others don't post, but I can tell you why I don't (and I'm not even a conservative):
1) I don't think HN should be a forum for political discussions in the first place; and
2) I'd probably just get downvoted anyway since the progressive bias here is so strong.