The same applies to comments on HN. Comments are not moderated based purely on legal or certain general "good manners" grounds, they are moderated to keep a certain kind of discourse level. For example, shallow jokes or meme comments are not generally allowed on HN. Comments that start discussing controversial topics, even if civil, are also discouraged when they are not on-topic.
Overall, HN is very much curated in the direction of a newspaper "letter to the editor" section, then more algorithmic and hands-off like the Facebook wall or TikTok feed. So there is no doubt whatsoever, I believe, that HN would be considered responsible for user content (and is, in fact, already pretty good at policing that in my experience, at least on the front page).
This is meaningfully different in kind from only excluding posts that reflect certain perspectives on such a conflict. Maintaining topicality is not imposing a bias.
Maintaining topicality is literally a bias. Excluding posts that reflect certain perspectives is censorship.
Or.. are you suggesting there's more to how this works? Is dang watching votes and then making decisions based on those votes?
"Editorial control" is more of a term of art and has a narrower definition then you're allowing for.