Was B what we know as a “reply person”?
I think it's not a question of scalability but the sensibility to develop skills needed to “read the room”. Just because the thread was public, doesn't mean it's appropriate to join. In many cases people post to share or vent and even if it sounds like a question, they probably don't want another opinion.
I am guessing, for the same reason I can have a picknick in the local park with a few friends and discuss intimate matters. This takes place in public because that is convenient, but I still don't appreciate random passers-by interjecting their opinion. It's fine to listen in though, if you're sitting close by. Most people intuitively understand this.
Online, this intuition sometimes disappears, and people feel that the fact that something is readable to them, implies it is meant for them to interact with.
a better example is a meetup in a closed room. (i just attended one of those). you are clearly part of the group, but you get to overhear private conversations, and sometimes it is appropriate to join in, and sometimes it isn't. the difference is that when i walk around the room from group to group, i get signals if i am welcome to join or i am being ignored. these signals are missing online.
But does the comparison really hold? IMO, you'd have to have your "intimate" public discussion carved in stone or something to be comparable. Your example is more like SnapChat or any other platform that limits the lifetime of postings.
Both your comment and the one you're replying to illustrate perfectly (if perhaps unconsciously) the problem I'm attempting to convey in the essay: Online interactions give the appearance to some of an intimate discussion whilst of a public discourse to others, and the clash of those perceptions quite frequently leads to unpleasant disagreement, frustration, conflict, and confusion.
People are supposed to read my opinions, but not have any of their own. They're supposed to give me attention, without taking any away from me. It's for their benefit, of course, but their words could never benefit me.
