Crime and Punishment

Locally a woman who shot her husband four times is trying to use a defense that she was essentially in a disassociated state when she learned that he was having an affair.  Additionally, she wants to plead that she has a disorder that basically makes her react in an exaggerated fashion in order to gain attention.

I'm really uncomfortable with this and similar defenses.  What if someone is a sociopath--other people basically aren't real and the only thrill this person feels is when they hurt or kill others or break the rules by stealing millions, etc.  Maybe they're considered insane.  Does that excuse them from their crimes?  What if they don't know what they're doing?  Does that mean that they should go free?  What then does such a person have to do in order to be removed from society so that they don't commit more crimes?  

This all just makes me think about our justice system.  I don't think any system is perfect.  I think there are issues no matter what you do.  I am concerned about the fact that in our society, violent predators thrive (or seem to.)  Is it because violent predators have always thrived, is my perception skewed, or is it because in our relatively safe society, we've intellectualized crime and justice so much that we haven't kept up with dealing with the reality of it?  In the process of being fair, have we forgotten the ideal of protecting people from crime?

I have no answers, only more and more questions.