How does one weigh human life?
When you say it like that, it makes me think of "weighing" one group of people against another group to decide which one is more important. I think that sort of thinking is dangerous. My answer would be "don't weigh it". The idea reminds me a lot of trolley problems (http://en.wikipedia.org/wiki/Trolley_problem) which generally offer only two choices, let group A die by default or kill group B to save them, with there being a catch to the choices (a lot of the times the catch is rather silly and unrealistic). I'm not saying that there can't be good, well-reasoned responses to such problems (my general approach to these problems revolves around determining why group A is the default to die, and whether group B could just as easily have been the default except for some minor circumstance of the problem. So yeah, I'll maybe flip switches but I won't push fat people in the way, for example), but when neither choice is any good I don't like the idea of forbidding some choices or requiring others.
Heck, here's a twist on one of the trolley problems: you're sitting beside some trolley tracks, watching 3 men working on the tracks some distance away, and you can see they're all listening to iPods so they can't hear anything. Suddenly you hear a trolley coming, and a fat man falls out of the sky onto the tracks. Looking up, you see a moralist standing on a bridge who looks rather shady. The fat man's alive but injured and can't get off the tracks unassisted. You now see the trolley approaching. Using your super deduction skills you realize that if the trolley hits the fat man it will stop and the workers will live while the fat man will be killed, but if you help the fat man off the tracks the workers will be killed by the trolley. Question: Do you save the fat man? Yeah, now the shoe is on the other foot, trolley problem.
Can we truly justify the death of any living being, regardless of the crimes they have committed?
Are we talking about the death penalty or self-defense here? I think self-defense is entirely justified.
And here's a good moral problem I heard a while back: You're in a lifeboat with a baby, a convicted felon, and a geriatric old man. You will be rescued, but not before you'd all starve to death. However, if the rest of you eat one passenger, you will live long enough to be rescued. Who do you kill and eat?
I agree with this answer (http://tailsteak.com/archive.php?num=497) but I don't believe there's any moral obligation to offer your own life. I do think mutual starvation is better than murdering one of the other three or being murdered.