There are many different views on such manners. In Iraq, when I went, there was no crime. You could get executed for being overheard insulting Saddam, I could never talk about him at all. We referred to him as "The Man". A murderer would get executed, no question, without evidence. In fact, all suspects for the murder got wiped out. So in that perspective, as harsh as the punishment was, there was no crime in Iraq!
The point is, killing them, though it can be said to be humanely immoral, can have benefits. There are too many sides to this argument, so it isn't really worth arguing over. As Turi says, when a murderer gets killed, you can't really pity him...