From our point of view as moderators, these subjects are not necessarily off topic on HN, but it depends on the specific article. Is it conducive to intellectual curiosity, the main value of this site (https://news.ycombinator.com/newsguidelines.html)? Or is it more focused on stirring up anger and rallying support to a cause? What's its information-to-indignation ratio? There isn't necessarily anything wrong with indignation—on the contrary, it can be very important in the larger social context, more important than most things on HN—but because its effect is to promote flamewar rather than intellectually curious discussion, we are more likely to moderate it here. We have to, or the site would soon go up in flames (i.e. become dominated by political battle), which would destroy the things it exists for.
The community is often in disagreement about which topics belong on HN. People who feel strongly about topic X tend to think that HN hasn't enough X and even that X is being suppressed. But frontpage space is the scarcest resource on the site. There isn't enough to go around, so every X ends up getting shortchanged. Beyond that, when a topic is repeated often enough, it becomes predictable, and predictability is the enemy of curiosity. We try to moderate HN for variety because the community strongly prefers that. My sense is that most of the time when X gets marked as [flagged], the flags are a sort of coalition between users who don't want to see X because they disagree with it, and users who actually agree with X but are tired of its predictability. If it were only the first group, there usually wouldn't be enough flags to win the tug-of-war against upvotes.
If you think an article is particularly substantive and shouldn't be marked as flagged on HN, you (i.e. anyone) are welcome to email us at hn@ycombinator.com so we can take a look.
In my experience, articles directly related to tech, like diversity in tech will stay open to comments for a long time before mods respond to flags and lock it, allowing a decent amount of discourse.
Articles that are science, but not directly related to tech (white supremicist shooting research) tend to be shut down faster if they are flagged. Why do users flag them? Probably because the arguments, potentially from either side make them uncomfortable and they’d rather it not be discussed here. The mods are just responding to user flags.
I have seen threads get uncivil, at which time the mods will lock them down, which I think is also fine.
Actually, the mods generally don't get involved in this at all. If an article is flagged by enough users it automatically gets killed (marked "[dead]"), at which point you can't add any more comments.
Sometimes the mods will revive a killed article if it's not off-topic and people ask for it to be reopened.
You can reach the moderators at hn@ycombinator.com if you have concerns about moderation issues.
See comment above, it appears to be automated.
That's correct: if a comment either (1) gets too many more downvotes than upvotes or (2) gets flagged, it's automatically killed.
Also, users can "vouch" for a dead comment or article to bring it back to life if they believe it has been wrongly killed.
I have a hunch some flaggers may not yet have enough karma to downvote, but enough to flag so they flag in lieu of downvoting but thats just a guess.
another thing to consider, is that HN comments do show up in google searches at times, so cleaning things up quick is a positive thing regarding, profanities, or potential liabilities.
Flagging is only supposed to be used for violations of site guidelines (off-topic, spam, uncivil or unsubstantive comment, duplicate submission, etc.), not for disagreement. People who flag on-topic articles or comments may get their flagging privileges revoked by the moderators.