[derefr]

But one of the interesting parts of the paradigm of hierarchically-threaded online discussion, is that only one subthread/reply to a given thread has to be a "productive conversation" (i.e. to continue the thread in the "obvious" way); the other subthreads can be tangents, and tangents do not "derail" in the same way they do in a flat-linear-threaded forum.

[mejari]

I would disagree, because they're still visible and still structurally part of the same conversation, meaning people reading the conversation will read those tangents, or at the very least be distracted by them.

[derefr]

And this is why subthreads in all hierarchical discussion systems are sorted by vote-rank: the subthread that most effectively serves as the continuation of the "canonical" conversation will (almost) always appear first. The only time that doesn't happen is when that subthread doesn't exist—as has happened here. More often than not, when this is seen in a "played out" archived discussion thread, this doesn't suggest that people are "getting distracted by" the tangent, but rather just suggests that nobody is all that interested in continuing the original conversation.

(Unless the tangent leads toward a mind-killing subject like politics. I'm 100% behind you on applying careful consideration before making a tangent from a technical topic to an emotionally-charged one; people see that kind of subthread and never even make it to the rest of the subthreads in the same conversation.)