The act of death penalty is nothing but primitive. People succumb to emotions of revenge and call them "justice", and make it seem right by giving a trial to either kill or not kill a human being. But that is all it is, killing. If you take justice by your own hand, it is revenge and murder, if a trial is done, it is justice. Why is that you ask? There is two simple reasons for this:
1. You aren't doing it yourself.
2. Everyone can agree that the person "deserves" to die.
Everything is hidden behind a false sense of logic in trying to kill a human, but its driven by emotion. Locking up someone for life has the same result as punishing someone with the death penalty. It cost less to kill someone you say? If you do a little research, you find out there is a lot of cost in trying to actually kill someone. Locking up someone prevents them from ever doing harm to society, from interfering with our everyday's life. Think about it, it all comes from rage, from emotion.
Personally, when it comes to judging, I disagree with the use of death penalty. It is simply too barbaric and it really slows down the process we slowly try to build. Heck, even religious morality allows the use of death sentence.
But I believe is different when it comes to "acts of war". A cop shooting a criminal who has been warned, or shooting criminals in the middle of a warfare is perfectly fine. During those times, the criminals are a risk to everyone, and may endanger the lives of the authorities, and thus proper action may have to be used. It is not the middle of a trial, it is in the middle of action, and thus "action" needs to be used. Action is different than trial, and must remain different.