What topics are those? When I hear claims like this, it usually turns out to be a topic that gets plenty of discussion on HN—just not as much as someone feels it should. It never feels like one's favorite topic gets discussed enough (see https://hn.algolia.com/?query=by:dang%20scarce&sort=byDate&d... for why), but that's not "it can't be discussed".
> But on Hacker News it has always been justified by it not being moderation.
We answer questions about moderation all day. When asked what happened to a submission, we say what happened. If users flagged it we say users flagged it. If we moderated it we say we moderated it. How do you get from that to something sinister?
> "It was flagged by users" is the common explanation.
Yes, because it is the common reason.