(downvotes incoming in 3...2...1....)
To see why it's a hard question, look at the two extremes of the solution space. One would be to ban every topic that you find politically provocative—i.e. that anybody finds politically provocative, since there's no reason to privilege one user over others. That would exclude most stories that get posted here—certainly everything about economics, history, philosophy, literature, city planning, etc., but also most stories about business and industry. Even many stories that appear purely technical would have to go. Probably everything would, once people got done being provoked by what remained. As some are fond of pointing out, everything is political when you get down to it.
The other extreme would be to allow every political topic and all escalations and flamewars. That would turn this place into scorched earth and kill it as a site for intellectual curiosity, its mandate (https://news.ycombinator.com/newsguidelines.html).
Since both extremes are impossible for HN, we need to draw a line somewhere. Where should it be? If we're optimizing for intellectual curiosity, we have to cast a wide net, because curiosity likes to meander. Any topic that supports intellectual curiosity is ok, even if it has political overlap. The topics that aren't ok are the ones that are (a) purely political, (b) purely sensational, (c) have usually turned into flamewars in the past.
What about stories that don't gratify your curiosity? Well, that's always the case, in the sense that no one likes every story and no story is liked by everyone. It suffices to gratify curiosity for some segment of the audience. If you run into one that doesn't work for you, there are plenty of others to read. If you run out, the 'past' link in the top bar is guaranteed to find popular threads that you missed. And if a submission really breaks the site guidelines, you can flag it. What's not ok is to start posting comments in the thread from a place of provocation rather than curiosity. That's not in the spirit of HN and the guidelines ask you not to.
All these concepts require interpretation, so any line we draw is fuzzy. Other moderators might make different calls. But the OP is obviously on topic by that standard, and while I understand how it can appear that we apply the rules selectively, I'd caution against leaping to a belief in moderation bias motivated by secret political preferences (inevitably opposed to your own of course! See https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu... (later edit: and >>26148870 )). All political sides get moderated and/or not moderated at times. When it comes to politics, the mods do something for everyone to dislike—which unfortunately distorts how people perceive moderation (https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...).
If you see a case that violates this standard, the likeliest explanation is that we didn't see it. We don't come close to seeing everything on HN. The second-likeliest explanation is that we thought it over and came up with some reason that is based on the site guidelines. Sometimes that leads to counterintuitive places. People are always welcome to ask.
If that's not enough, there are plenty of prior explanations: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so.... Take a look, and if there's still something I haven't addressed, I'd be curious to know what it is.