We all respond in any discussion, and live life in general, according to the spirit under which we operate as individuals. The natural man is naturally selfish. Thus he will respond defensively. The natural selfish man is naturally predisposed to self preservation. Thus he will respond in a manner which preserves pride, upholds his status, retains ego. And he will go to any lengths to do it. Even to going on the attack to put others down in order to create an impression, even if it is in his own mind only, that he is winning. The selfless man however, will be more inclined to put forth his arguments in a discussion, or provide what he believes will provide for others, regardless of self interest, with other peoples best interests in mind even if it costs themselves status, pride, or reputation. Such folk are always open to discussing matters with an open mind, willing to explain their points without promoting self, allowing what they offer to stand on their own merits. Even to be willing to leave a discussion if it means no further ground can be gained if it means peoples personal boundaries are being compromised. Even truth should never be used to destroy others, but to enlighten. Wisdom is in knowing the difference.
Foregoing the references to different sides going in different directions, this an excellent post, and well communicated. And in sympathy for all believers, we do all come by happenstance from different perspectives in what we believe and have learned from God. The trick is in learning to see things from other people's perspectives, while still maintaining our own mind on matters.
It must be conceded that it is natural to be defensive, as you say. I found that the stronger I became in my doctrinal beliefs the less defensive I became. But I also developed the humility to admit the weaknesses inherent in my positions. For instance, when the world tries to tell me that the church is full of hypocrites and judgmental types, I usually just agree with them, LoL. But at the same time I present the other side of the coin; that there are plenty out there who are very genuine, and seeking to serve God as faithfully as they know how every day. This has a way of catching them off guard, because they were expecting contentious contradiction and instead got someone conceding their point.
It's the same way in debates, imo. If we have humility, it makes us able to concede a point now and then. But now this is why the topic addressed in this thread becomes so important. Who wants to concede a point to someone when they're already insulting and mocking you? What would any sane person expect to receive from someone who is already trying to make you look like a fool? I will nevertheless do so on occasion, but it does take both a humility to admit to not knowing everything and also to withstand being mocked all the more. And I think matters could be made so much easier where reconciling with others were concerned if derisiveness was eliminated from the conversation altogether. Then both parties might feel a little more at ease about occasionally admitting maybe they were wrong about something.