George Orwell 
The Lion and the Unicorn 

As I write, highly civilized human beings are flying overhead, trying to kill me.

They do not feel any enmity against me as an individual, nor I against them. They are 'only doing their duty’, as the saying goes. Most of them, I have no doubt, are kind-hearted law-abiding men who would never dream of committing murder in private life. On the other hand, if one of them succeeds in blowing me to pieces with a well-placed bomb, he will never sleep any the worse for it. He is serving his country, which has the power to absolve him from evil.