As a fella who spent a awful lot of my parent's money getting a degree in philosophy from an expensive school, let's just say it's a really complicated issue addressable from a variety of angles. And there are a lot of assumptions running underneath most of the replies here that could devolve in to huge threads of their own. And I would suspect many don't even realize the assumptions or problems these sorts of question raise when you drill deeper.
There is a fantastic entry level course covering many of these issues called "Justice". They are a series of lectures by Michael Sandel of Harvard and they are really quite good. The first few involve killing and he dives in to the assumptions we made and the discomfort we feel over some of these issues. Strongly recommended. There are 12 lectures, all very good, by the end you're getting deeply in to Kant, Locke, Aristotle, Rawls, et al. All free and one great thing about the lectures is that he regularly engages the students in the audience to get their thoughts and feedback. Which helps drive the discussion in a rather Socratic fashion.
Free on-line and well worth the time if you're in to digging deeper.
http://www.justiceharvard.org/
Have a lovely Fourth of July all you US folk in the discussion. And to fellas like Kevin, as always, thank you again for what you do for all of us.