I have many good friends who are pacifists, but I am not.
This was an issue I had to wrestle with when I became a Christian whilst serving in the Australian Army.
But I do appreciate the force of pacifist arguments.
Jesus taught about turning the other cheek, non-retaliation, and love of enemies.
In much of early church history there was either a prohibition against serving in the military or else deep moral ambivalence about military service for Christians.
You cannot defeat violence with even more violence.
Most wars are unjust and the innocent suffer as a result.
I think World War I is the best example of pointless, stupid, bloody war that should never have happened.
Probably the best argument for pacifism comes from Miroslav Volf who argues that divine retribution against evil is the grounds for Christians to renounce repaying evil for evil. It is a good quote:
"[I]n a world of violence it would not be worthy of God not to wield the sword; if God were not angry at injustice and deception and did not make the final end to violence God would not be worthy of our worship .... My Thesis that the practice of nonviolence requires a belief in divine vengeance will be unpopular with many Christians, especially theologians in the West. To the person inclined to dismiss it, I suggest imagining that you are delivering a lecture in a war zone ... Among your listeners are people whose cities and villages have been first plundered, then burned and leveled to the ground, whose daughters and sisters have been raped, whose fathers and brothers have had their throats slit. The topic of the lecture: a Christian attitude toward violence. The thesis: we should not retaliate since God is perfect noncoercive love. Soon you would discover that it takes the quiet of a suburban home for the birth of the thesis that human nonviolence corresponds to God's refusal to judge. In a scorched land, soaked in the blood of the innocent, it will invariably die. And as one watches it die, one will do well to reflect about many other pleasant captivities of the liberal mind."
Miroslav Volf, Exclusion and Embrace: A Theological Exploration of Identity, Otherness, and Reconciliation (Nashville: Abingdon, 1996); 303-304.
However, I cannot bring myself to be a pacifist, because I do not think it wise or possible in a world of evil.
For me, I did not consent to military service so I could fight for God, king, and country; much less for empire, oil, capitalism, imposing democracy on some Arabs, because of personal rivalry between European aristocrats, or for some God-forsaken rock in the South Atlantic.
I believe Christians can serve in the military because I believe in nations having a military for self-defence and to aid other nations who face needless and unprovoked aggression.
I say this because: