The police and the military in America do not have the authority to kill anyone they think is a bad guy even if he is a child rapist or a murderer. In America the system of justice has a well defined process to make sure that innocent people are not punished for crimes they did not commit. "Innocent until proven guilty," etc.
Even in the terrible fog of warfare like in Vietnam, Iraq, or Afghanistan soldiers have to be very careful that they do not violate the human rights of the people that are confronting them. Certainly they cannot just on the spur of the moment decide to kill someone who might be a bad person. If they treat people improperly they risk their careers and perhaps risk going to jail.
So how does America justify the increasing killing done by remotely controlled drone aircraft? If a mistake is made, and innocent people die, who do we hold accountable? In a democracy this is vital. Our self image does not allow us to think of ourselves in the same way that we think about the Nazi SS storm troopers or the KGB. I am having a hard time working out how these drones and missiles can legally be utilized to kill people when remotely controlled by people thousands of miles away. Doing it by remote control makes all this killing far too anonymous. There is something really wrong about all this that I am having a hard time defining.