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....)