I'm a disagreer and I have to disagree with the authors: disagreeing is not trolling, it's countering trolls. Trolls usually flood the zone with comments that seem elaborate but are ultimately low effort. They know persistence is key, so they don't bother much with replies that counter their claims; rather, they focus on those in agreement to manufacture consent.
It might look sinister if someone drops a reply and leaves, but that alone tells you nothing. In my experience, there is always Brandolini's law at play:
> The amount of energy needed to refute bullshit is an order of magnitude bigger than that needed to produce it.
If a reply takes a lot of effort and if you suspect the other side isn't arguing in good faith, one reply already feels like a waste of time and there's no reason to go for round two.