I have to say that the comments in this thread are so thoughtful. I am a flaming liberal who never owned a gun until 50+ years of age. I do now because of all the reasons you already know. My husband was the one who said we should do this and he didn't mean just for himself. He spent weeks discussing why it was just as important for me to have and know how to use a firearm as him. I was frightened by the whole idea. But he calmly and patiently discussed it with me for weeks. We went for training, did lots of reading, and what surprised me most (as a liberal who had the typical guns are unnecessary for average citizens) was the kind of talk that I see in this post. Rational, sane, logical, thoughtful, considerate, non-macho, talk. I am amazed at how my view of guns and "gun-toting" people was so skewed. And I know it's because of a) the media (movies and tv portrayal of the use of weapons is just odd sometimes) and b) because no one in my family owned or used or talked about guns as a form of self-protection.
I have always had a knee-jerk negative reaction to the kinds of rhetoric from gun lobby organizations or single issue organizations. Of course now I see the value in them, but my point is their arguments never convinced me. This kind of discussion, calm and rational, is what contributed to my change of heart. So the advice given here about taking your time to discuss your particular issue with your wife and bringing her into the training and getting her comfortable with the gun culture, seems very sound to me.