Very interesting read. One element I would like to add, which came to me during my time studying communication and the effects of propaganda, is the underlying concept of motivation and intent in regard to how someone might communicate during discussion and frame the delivery of their intended message, or guide it to the outcome they want.
As per your above argument, we tend to assume during most active discussions that the beliefs, opinions, and attitudes of those engaged in the activity are based on some sort of internal logic (whether or not that logic is substantiated through evidence and reason), and that, even though their reactions are guided by past experiences and beliefs, the responses you receive are generally spontaneous and in the moment, not planned or constructed or motivated before hand. Rarely do we give much thought to what active intentions and/or conscious or subconscious motivations may play a role in someone's ability or inability to accommodate the cognitive dissonance you mentioned above, or their willingness to adapt and change rather than retreat from, or intervene in, the flow of the conversation to alter its outcome.
We all harbor biases and experiences that create the individual realities you discussed, but we sometimes don't consider how unknowingly powerful those biases and experiences can be when they play into tough situations and/or uncomfortable discussion (or challenge something someone needs or wants to be true).
When these motivations come from knowingly, actively influencing discourse they can be even more powerful, especially if other members are unaware of its happening. Such influences don't necessarily have to be overtly malicious in nature, only an underlying motivation or need that guides someone's stance in a conversation for private reasons -- it is actually one of the fundamental aspects of critical discussion over passive sharing of opinion.
Intent and motivation are powerful forms of influence that can dictate, at a fundamental level, the very nature of communication and discussion. Sometimes, internal (and perhaps unknown) influences can interfere before a discussion becomes productive -- and make it difficult or impossible for some people to overcome even active, critical attempts to open themselves up to alternative view points (I've personally witnessed people completely give themselves over to an idea and accept it only to discard it in practice due to it challenging them on an emotional level, even when mentally they new the opposite to be true -- this is probably one of the hardest types of people to have critical discussion with)
I think this aspect of discussion is just as important as any other, being mindful of such influences. An effective member of a discussion has to spend equal if not more time in consideration of the positions of other group members, and other peoples reactions to the conversation, as they do their own. Only then will they be mindful of barriers that are going up or aware of other intentions that may be influencing the outcome of the conversation (or know when to walk away). This is probably more important than any concrete, fact-only based arguments: the flexibility to know when and how to step forward (or back) and lean more on emotion, or reason, or fact, without being dishonest in what you want to accomplish, or letting other vent or retreat when necessary, in an effort to keep a beneficial dialogue moving forward.
So I guess my, hopeful, contribution to this conversation, is that most successful discussions don't really come from defending your own personal beliefs and opinions, but by actively understanding those of the people you engage. Only then can you truly construct an argument that they will accept, or successfully challenge their beliefs (You know, if that is the intent that motivates you to engage in discussion with them).