Police and military take lives of others all the time on a needed basis.
Just my 0.02
Those are the only two institutions allowed to use force (ie. physical violence or even death) within a society and at the same time being considered heroes. In fact, the state is the only institution that has the right to kill anyone and defines who can kill people and who cannot.
People that enforce the laws and will of the state are allowed to kill other people depending on the circumstances. Anyone else (not related to the state apparatus and/or acts on behalf of someone or some entity other than the state) who kills people, the state considers such person as a murderer or a criminal and the result is punishment for committing an act exclusively reserved for the government, unless it can be proven that an individual killed someone else in self defense.
In fact, the only difference between a criminal and a military soldier, for example, is that one acts on behalf of someone other than the state while the other acts on behalf of the state. The former is considered a potential rival to the power of the state and is the target of state violence and restrictions (ie. gets arrested and thrown to jail, gets death penalty in some countries, etc) while the latter the state considers a brave hero.
Everything taught to you through religious teachings and through education on morality, accepted public conduct, what's right and what's wrong is irrelevant because all of those ideas indoctrinated into peoples minds all achieve one simple thing:
The dominance of the state over their lives and territory and the refute of anyone who does anything that may challenge the authority of the state. For this reason most people can't tell the difference between a criminal and a police officer/army soldier; and despite both doing the exact same thing (kill people), the general public tend to have different emotions and opinions regarding both types.
This is all part of the social construct (a fancy word for lie) that is created in the minds of people in order to ensure that the status quo (ie. power and control of resources by a group of people) is maintained. This and other things such as nationalism keeps modern society and civilization in relative stability as far as its own survival is concerned.
-NALs