Death Penalty

Furthermore, we don't kill people for protection. We kill people so we feel that we have the right to pass moral judgment on them. For instance, he who is declared mentally insane, with no hope of rehabilitation, is allowed to live, albeit in a mental facility. He has no hope, as far as we know, to be rehabilitated. He is more of a danger to society on the outside than a mentally competent person who let his emotions get the better of him. Yet he's kept alive.

Warfare is a perfect example of how we kill people for protection, especially in defense. Your mental facility conjecture isn't quite accurate as it doesn't suggest that the insane person had ended another's life. I also would believe in a lesser punishment for a 'crime of passion' as you describe instead of a first-degree murder, but this can be easily exploited.

I also am a believer in that a person should have the right to determine the time and manner of their death, if they so choose. I suppose I'm a little more cavalier regarding human life than others.