And even in those rare political posts I find, the discourse is very different from other places. I think that boils down to the golden rule of comments: "thoughtful and substantive". I've noticed the culture of HN is to downvote any comment that does not adhere to this rule, regardless of whether you agree with it or not. Even in comments I've posted about China that ended with a sentence about how I disliked the leader got knocked for being counterproductive.
At the end of the day, you can have the most frought and divisive thread here and the comments are going to all be far more civil and thoughful than on Reddit or Facebook because even thought everyone might be up in arms, all of them are going "well I'll show them! types long thoughtful comment that addresses everyone's grievances"
I think one issue with approach by up/down voters is that sometimes the "thoughtful and substantive" thing to say is inherently ideological, and I notice that being explicitly ideological (for example, making it clear that you regard a long term trend in the economy as serving the interests of a particular group of people) is viewed as counterproductive.
This mirrors a dilemma out in the "real world" where people find it hard to bring up substantive political ideas because just doing that is viewed as divisive and antagonistic. Unfortunately, sometimes (maybe even often) this is actually what is required to have "thoughtful and substantive" discussions.