It's possible to be frightfully effective in such an argument, but the methods you have to use feel pretty dirty, because they are. If you can force people to defend indefensible implications of their position, you score points. If you can trick a bunch of opponents into saying something obviously stupid, you score points. If you can find a loud idiot and make a fool of them in public, so that the lurkers don't want to be associated with him, you score big. And often pure typing speed helps; if you're answering the same arguments again and again, you can fire off a lot of replies very fast, flying on autopilot. A handful of vocal people using such tactics can change the default views of a whole forum. It works.

That's the kind of methods we should get good at calling out here. I'm not sure we are yet. The skills for group rationality are different from those for individual rationality, which are those that have been discussed the most here.

Listing the dirty, dark-arts techniques is a good first step towards fighting them.