In a time of world war 2 there were a number of Christians in high positions in the British Army, including Sir William Dobbie of the brethren. Peter Masters has a chapter in a book about his heroics, but I give another link with brief detail.
The army and the police force are necessary for law and order and the protection of society and God's instrument to protect families and individuals. Sometimes force is necessary and justified.
Let us suppose a terrorist is caught and has information that will stop the deaths of thousands. Is torture justified to save the many, or do we turn the other cheek? Should the police gun his friend down who is ready to detonate a bomb?
A big man is stabbing women and children in a shopping mall. He has just stabbed a policeman, the only man in the mall, except me. I have in my possession a snow shovel. I could hit him over the head from behind and possibly kill him, or walk on by and go home to clear the snow.
I would pray that the Lord would help David defeat Goliath and if my own actions saved many and slayed a violent murderer, do you think my actions be right or wrong?