Following standard ideological grooves to discredit the other tribe's sources is not acting from specialist knowledge in any case. The only specialty at work in such discussion is the specialty of internet battle. That's ultimately just a way to turn every thread into a boring, if intense, flamewar.
One of the things that follows from HN's core principle of intellectual curiosity (https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...) is the principle of diffs (https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...). Diffs are what's interesting. This is the positive formulation of the principle that repetition is bad for curiosity (https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...).
For topics that burn hot, like political/ideological ones, this "diff" principle implies that discussion is most interesting (and therefore best for HN) when people don't take the obvious path from their own initial position—that is, when they don't repeat the reaction that they've had most often before. That is a hard thing to ask on the hottest topics, which tend to melt into a few (well, two) monolithic piles of tar. But I think it follows from the principle.
Here's another thing that I think follows, and is even harder to swallow. To the extent that someone has strong political/ideological views, if they're not seeing articles on HN that they strongly disagree with, at least semi-regularly, then there's probably something wrong with HN*.
That isn't always great for community spirit because it only takes a few disagreeable data points before the mind starts to defend itself with a "this place sucks" reaction (and there are people on all ideological sides who develop such reactions). I wrote about this here, if anyone wants to read more: https://news.ycombinator.com/item?id=23308098.
* To ward off one common misunderstanding: that is not a Goldilocks argument for split-the-difference centrism! It's an argument for unpredictability. Since centrism is just as predictable as other ideologies, it should encounter just as much to be put off by.
No, if you look in the site guidelines you'll see that they say "Most" stories on certain themes are off topic, and that word is there intentionally. It allows for exceptions, especially when there's either something interestingly different about a story, or some significant new information to discuss.
https://news.ycombinator.com/newsguidelines.html
For past explanations about how we think about this in terms of political topics, see https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so.... There are lots of links there to where I've explained this in detail. If anyone has a question that I haven't answered there, I'd be happy to take a crack at it.
Stories drawn from the arts, like music and also literature and painting, or more generally from history, archaeology, you name it, are most welcome here as long as they offer something of intellectual curiosity. So if HN commenters are pushing back on a story just because it's about e.g. music, that would be bad. (But if it were a gossipy story about a famous musician, say, that would be different.)
Sex is its own special case in all things, so we would have to talk about that separately.
That's a fine principle. By extension, it should also be fine for commenters to note facts about sources. You are right that internet discussion can be derailed by the DAG of association, but internet discussion based solely on "what does the article say?" is naïve, amounting to borderline sealioning.
Part of critical thinking and reading is understanding the POV of the author(s) and publisher(s), and considering their motivations and incentives.
I don't think the DAG-of-shame game really has to do with curiosity about facts. It has to do with tarring ideological enemies. Maybe they deserve it, maybe they don't, but it's not the quality of discussion we want here.
Rather than an ambiguous phrase like "noting facts about sources", I think we're better off applying the clearer distinction between curious conversation and ideological battle. There's a binary distinction between those two things (as binary as these things can get), and we know which one we want on this site.
Moreover, one destroys the other, so it needs to be actively moderated. I don't just mean what moderators do, but the general sense of dampening excesses and avoiding extremes. We want a culture of moderation on HN—not for its own sake, but because curiosity only flowers in a temperate climate.
(By the way, I'm not disagreeing ideologically with any of the comments that I'm objecting to here. This is about discussion quality and attempting to organize the site around one specific value: https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor....)