On the other hand, I feel like some people have internalized this idea a bit too well, and apply it in places it doesn’t belong, becoming offended (for social-norm-violation reasons) when someone gives a tangential reply in a threaded comment system like HN’s or Reddit’s, because the tangent is “derailing the conversation” or “not addressing the topic.”

Except, of course, that’s impossible; a tangential reply likely won’t even be the first reply people see in the sub-thread, after they get re-sorted by vote, so the only people who will engage with it are the people who never cared about the original topic in the first place.