Having a civil conversation is about mutual listening and mutual respect.
Sometimes that gets conflated with affect — people act like the defining feature of respectful conversation is things like the position of your body, the volume of your voice, and whether you’re using polite words.
Sometimes things like that can be involved in what makes a conversation respectful, but they don’t define it.
The rules of politeness allow people to be dismissive and cruel. Similarly, it is possible to have a mutually respectful conversation that violates the rules of politeness.
For instance, it is often possible to have a mutually respectful conversation with raised voices and cuss words. It is also often possible to use a lot of I-statements and gentle-sounding language to have a conversation that is fundamentally disrespectful and cruel.
Conflating affect with respect ends up drowning out a lot of voices, and privileging people who are good at manipulating the rules of politeness.
(Affect matters, and it’s ok if some kinds of affect are dealbreaking for you in terms of your ability to have conversations with someone. I’m not saying that everything should be acceptable to everyone. All I’m saying is that affecting politeness is not the same as treating someone respectfully.)
Short version: Body language, tone of voice, and affect can be part of what makes a conversation civil and mutually respectful, but they don’t define it.