You probably already know this in your gut, but whether you are at the beginning of an argument or deeply into one with another person, becoming defensive nearly always ups the ante. Becoming defensive triggers a reaction in your co-fighter often to become more aggressive. Relationships are hard, sometimes on a daily basis. I came across this article today and felt it was definitely worthy of sharing.
Speaking of sharing, much of this is about sharing power in a relationship and how important this is. This article skims only the tiniest surface of Dr. Gottman's insight. He is a researcher that has produced a vast wealth of knowledge about what makes couples successful, and has over 90% accuracy in predicting divorce in couples he observes. He describes "the four horsemen" that are highly destructive in relationships: criticism, defensiveness, stonewalling, and contempt. If these elements are present the relationship can spiral downward quickly, but couples that engage in reparative attempts can still save the marriage. He describes this and much more in his book The Seven Principles for Making Marriage Work, which is a book that I highly recommend. If you want just a taste of some of his work, read this article.