I find this to be a very false stereotype. I find it an emotional decision to be cruel. Or even mean to others. For example, I am not an intentional asshole. It's accidental due to insensitivity to people's feelings and ideologies or whatever.
It's all about efficiency. For example, when we hunted down terrorists in the Middle East, or captured saddam hussein, my strategy would be kill on sight. No fuss, no drama, no wasted time and resources bickering about jail sentences, protection, fair trial, etc.
1 bullet. Case closed.