I cannot remember the author who came up with the I-thou and I-it relationships, but it’s usually used in regards to stereotypes and prejudices. For example, instead of viewing someone as an person of a certain race and base my judgments solely upon that (an I-it relationship), I should view them as a whole person and discuss and learn from them (I-thou relationship).
I wonder if this can’t be applied to argumentation. Perhaps the reason some arguments are overly agonistic is because the arguer views his adversary in an I-it manner instead of an I-thou manner? I’m not sure, and it’s an idea that just popped into my head as I was reading some Quintilian (which, I begin to ask myself, how closely am I paying attention to Quintilian’s text?). So, if we view our “adversaries,” or those who agree with us in an I-thou manner, would be get more listening, less agonism?
Martin Buber wrote about I-Thou and I-It!
And James Moffett talks about I-you and I-it relationships. I haven’t read his Teaching the Universe of Discourse but Lindemann talks about his theories in her chapter on Cognition.
Anyway, yeah — maybe we should sometimes use the word “you” more than the “audience,” especially when talking about writing arguments. “Audience” can tend to sound like a group, which may tend to let writers think in terms of the group as an “it,” like you said.