I would fallow the principle:
Man started killing millions of birds because those got infected with bird-flu: birds are threat to humans.
Man started killing millions of cows because those got infected with Mad Cow:cows are threat to humans.
So, why do not we kill all the humans who are a threat to other humans?

Often I encountered the words crazy/madman. Some people who have mental disorders, find it quite normal to do wrong things on others. Are they insane, lunatic, crazy, mad, if they find it normal?

Today, we do not find sacrifice and cannibalism a normal thing. Nonetheless the Aztecs found it perfectly normal. So the whole population was composed of madmen/lunatics? I don't think so, it was, simply... culture!
What to do with those who find it normal and have done a crime worth of the death penalty?

Hello, I am new to this forum and you will find that I tend to be terse in my replies. Firstly, I do not think that any State should have the right to put anyone to death(including war). Secondly, as has been stated previously, no system is perfect. And because of this, a guiding principle since the days of the Magna Carta has been "that it is better that nine guilty men should go free than one innocent man should be condemned".

Right or wrong on many occassions ide be willing to kill and i hate the thought of taking another's life. Is there ever a reason to kill ? i think so ..What amazes me is how many convicted murderers would prefer death to a life in prison so whats worse execution or incarceration? Taking ones life away can mean more than killing them ,it could be called taking life by excluding them from living.