For my part I think it's asynchronous written debates that are the source of these problems, so even earlier than facebook.
On a large massive forums, people write for themselves, not the others, and barely read the discussion. Oral debates or written rendering of them, had the advantage to be slow, less variate, and adaptative to a single argumentative line.
Nowadays when you discuss an issue online, everyone starts new train of thought to escape adaptation, and care little about an audience they d need to seduce or convince.
I suppose I just did the same anyway, you can reply but I wont read :)