The Macho Paradox

I am enjoying reading bits of The Macho Paradox: Why Some Men Hurt Women And How All Men Can Help and discussing the ideas presented with Cody. As a man, he is (naturally) defensive at first, but I find it entertaining - as well as good practice for me - to work the defensiveness out of him until he acknowledges the truths of the issue.
Do you suppose men are so defensive when the subject of violence against women is brought up simply because they are men? I don't quite understand it. Perhaps a reversed example would be useful!