I've never seen my parents argue. I've never even seen them raise their voices at one another. This is not to say they never disagree about anything, but they have enough respect for the family to keep private matters behind closed doors.
I attribute this to the fact that my Father is perhaps the most relaxed human being I've ever met, only showing anger when my sister or I did something incredibly stupid. And even then, from him, we usually received a hard, unnerving stare that said more "I'm disappointed in you," than "I'm about to send you home to Jesus." That, and a lecture. The longest lectures ever. Always. Many times, we'd secretly wish he'd just slap us one good time and get it over with. When it did happen, he disciplined us as if he felt sorry for us, or because he knew that his "beating" vs. Mom's attack was a favor, indeed.
As I mature, I have realized that this is why I can't remember the last time I raised my voice at anyone in anger. My Dad and I aren't passive, just nonconfrontational and, usually, rational. Now, I'm thankful for this trait. Unlike when I was younger, I'm certain the level-headed approach has helped me steer clear of many potentially bad situations. I can remember hearing Dad comment once, in regards to deciding against anger, "What's the point?"
True words, indeed.