...wherein I channel Yudkowsky...
There are two goals one might have when engaging in an argument. The first is to defend one's own position, and/or score rhetorical points. The second is to better understand the opposing point of view.
In different words, when attempting to understanding the world, there tend to be three activities one might be doing. One might be attempting to discover what is interesting; one might be attempting to comprehend the opposing position; one might be trying to determine the limitations or truthiness of the position.
Of course, one also might be doing something else besides attempting to understand: defending, arguing, trying to win a discussion, advocating, playing social games, being polite, etc.
This blogger's inclination is to believe that (due in no large part to the extensive practice of rhetoric on the part of most arguers) once one shifts into the rhetorical/argumentative position, one has frequently exited the discovery and comprehension phases. Is this always true? No. Is it tremendously hard to manage simultenaity? Yeah. Roughly, I almost never see anyone do so.
Another point borrowed from Eliezer is that if one is to really pursue truth...it is insufficient to argue against your strawman parody of an opposing position, but rather against the most intelligent version of the opposition that you can conceive of. Sure, sucks for scoring cheap rhetorical points. But makes for a much more in depth pursuit of truth.