One of the best parts of a deepening relationship with someone is the comfort to express your beliefs and points of view most openly. Of course, this also sets the potential for some of life's largest disagreements. Often, dialogue breaks down to dogmatism.
The real question seems to be how do you advocate for your point of view without being "defensive?"
Defending a perspective is good - it shows you are well reasoned in your beliefs. Being defensive implies something has broken down where you are dug into your point of view and can no longer hear anyone else.
Defensiveness has three common signs:
Emotionality - we enter into a triggered state. Our fight/flight instincts get activated, we can hear the blood rushing in our ears.
Absence of curiosity - We become unable to listen to the other person's point of view. We are so focused on why we are right that we cannot hear what the other person is actually saying.
Dogmatism - We are unable to contemplate the weaknesses in our own argument.
All of this is made ever more challenging by the fact that too often, we do not plan on getting into this sort of conversation. It may just bubble up, often as part of an emotionally intense dialogue.
How then do we handle these sorts of conversations?
First, learn to self-monitor your emotional state and get distance in the moment if need be. As our passions get aroused, too often we lose the ability for rational thought. It is a learned skill to observe this happening and interrupt the cycle.
Second, when someone is speaking - listen for understanding first. Do you understand what they are saying? See if that is true by repeating back what they are saying and asking for clarification.
Third, acknowledge their humanity. Appreciate the time/effort/concern they bring to their point of view. Even if you couldn't disagree anymore, there is still a human being there.
Fourth, share your perspective and where you disagree and why. Simply speaking louder is not a reason why.
Finally, end the dialogue. Sometimes a conversation changes a mind. Sometimes we just like to be heard. The real question - can we hold our views and still retain the respect and remain in relationship with someone holding a dramatically different view?
Here are a few books that are well worth a read:
Crucial Conversations: Tools for Talking When Stakes are High
Supercommunicators: How to Unlock the Secret Language of Connection