The answer is we all have different callings and purposes for being on earth. Christ came into the world as a sacrifice. It was his mission to be a martyr.
John 1:29 - Behold, the Lamb of God, who takes away the sin of the world.
1 Peter 1:18-19 - You were redeemed...with the precious blood of Christ, a Lamb without blemish or defect.
Revelation 5:6 - Then I saw a Lamb, looking as it had been slain, standing in the center of the throne.
Jesus asks his followers to forgive all things, but this leads to lawlessness if imitated on a large scale. If our drug addict friend steals from us, is it a good idea to forgive him again and again? A nation of Christian martyrs would be quickly invaded and crucified by the enemy. God gave the nation of Israel the right to territory and self-defense. Otherwise it could not exist.
On the most elemental level, no town can exist without laws and law enforcement; which means penalties for violators. A large segment of the population obeys the law only for fear of punishment. Successful cities must have small armies of police vigorously enforcing the laws, and a sophisticated judicial system to determine guilt and punishment. Consequences must be severe for serious crimes; which means violence of one kind or another.
Armies are a national police force, designed to deter enemies, aid allies, and enforce national policies; except in those instances when a nation deliberately attacks a neighbor and seizes territory. Wars are almost always law enforcement actions, regardless of the reasons or excuses given.
Pacifists who cry for unilateral disarmament are a menace to their nation and actually encourage war and tyranny. Many delusional people believe that all we have to do is "set an example", and others will follow. That is, if we lead a virtuous life and disarm our nation, recycle our garbage, get rid of our cars and ride buses, the rest of the world will imitate us. They have a very inflated opinion of themselves and their influence on others.
The world does not work that way. Different cultures all over the globe have radically different modes of thought. Self interest or tribal loyalty in the narrowest sense governs almost all behavior. Only the fear of severe punishment keeps the world's rogue nations and mobs at bay.
Much of the world does not respect or admire Christian non-violence. Those who have been most successful with non-violence - Mahatma Gandhi, Martin Luther King, and Nelson Mandela - were battling western, largely Christian, and educated authorities. If these great men were dealing with the totalitarian regimes of the east, they would have been murdered wholesale.
Our answer is clear. Unless we have a calling to be a martyr, we have every right to defend ourselves, personally or nationally, with violence if necessary.
Conscience should guide us, however. Traditional western rules of war established over the centuries must be observed, or we risk losing our souls. Justice and mercy go hand-in-hand. Vengeful or thoughtless cruelty and enjoyment of an enemy's suffering is a mark of Satan, our ultimate adversary.