How can someone be so heartless and send people to die?

I'm sure you know about the holocaust. But the thing i want to know is how can one person be so cold and heartless to sent people to a concentration camp (death). Don't they think about anyone other than themselves? Obviously they don't. It bugs me to know that people can purposely kill and still sleep at night. If I ever kill someone, or even hurt anyone, I would not be able to function, I would feel too bad, not only for the person, but their family. Honestly, I wish I never know what it takes to kill and not feel a thing. I hear about all these deaths and it makes me sick just thinking about it. All though, I don't think the people that are fighting in Iraq and Afghanistan should be punished because they are fighting to protect their country and the people that are in it. If you ask me, it's all stupid. Yeah, there are gonna be people in this world that your not going to get along with, but you don't go out and kill them. You can let them know that you don't like them, but by words.