Let's pose a hypothetical situation. Your next door neighbor is robbing you every day. His method is to walk into your house with a large group of armed thugs who hold you at gunpoint while he takes what he wants from your home. You know for a fact he will keep doing this every day until you make him stop because he tells you he will. You can't call the police because they ARE the group of armed thugs. What are you to do? You can't put him in jail. You can't kill him when he is directly threatening you because he has more guns. It seems to me that the most logical course of action is to kill him when he isn't expecting it, not when he's directly attacking you. The fact that his declared intentions are to steal from you every day is key, because it makes anything you do to him an action of self defense. It's somewhat similar to a robber who says, "Give me your watch or I'll cap your ass." He hasn't yet attacked you in any manner other than verbally, but it's your right to shoot him in the face to keep him from taking your possessions or capping your ass in the future.
I'm not going to shoot the mailman because he thought he finally nailed a great job because it comes with a sweet benefits package. That's absurd.
Neither do I plan to shoot the mailman. He likely doesn't realize that he is paid through violence and theft. That doesn't change the fact thay by my moral code, his life is forfeit. I would rather have him work off his debt to me, but the situation in which we all live makes this impossible. If I were to take his life, I would be defending my belongings from him. (I'm working off of the idea that the mailman makes his money through taxation in this scenario, which I'm not sure is entirely true.) I am not an advocate of killing every person you feel you have a right to kill. For instance, I've been attacked by a drunk redneck while I was armed. (Hooray for the shithole town of Kirksville, MO) I didn't even pull out my weapon. He was trashed and barely able to stand up, so I kicked his ass instead. It was easier on my psyche than shooting him would have been even though he attacked me from behind. In my mind, his life was forfeit to me, but I chose not to take it because I am merciful. However, if my friend kills someone who they have a right to defend themselves from, it would be wrong of me to turn that friend in.