That's all nice and well, but then the person killing the killer should forfeit their right to live also...
My point is this:
We no longer live in a society where nature can kill you at any opportunity with little warning. Our society discusses and debates. While I understand the feeling behind the sentiment, it does little to create harmony.
Another point is that if you look at the animal kingdom, there is no concept of an eye-for-and-eye. The Lion killing an Antilope does not get set upon by the family of the Antilope.