No one had ever killed without a justifican at least to himself. People who believe themselves to be good justfiy killing to mitigate the guilt they feel, people who are not good justify to clear their image. Justification doesn’t make someone less criminal than any serial killer.
Usually governments use their armies to achieve some hidden agendas and what they need is a good fake story to make their war legitimate and what is more legitimate than their people freedom and security.
On the other hand many of the victims families believe that the people of a country are as responsible as their governments of the killings because they had elected them and pay the money used for the killing of their family members. If you have ever watched a video by terrorists they use this as justification for killing civilians.
And if you join the army and willingly kill for your government’s hidden agenda you should be held responsibly for your deeds too.
“ I was just following orders” is no excuse