Don’t you know it is wrong to kill? Yes. But you do it? Yes. And you still believe absolutely that your cause is right? Yes.
It is right, he told himself, not reassuringly, but proudly. I believe in the people and their right to govern themselves as they wish. But you mustn’t believe in killing, he told himself. You must do it as a necessity but you must not believe in it. If you believe in it the whole thing is wrong.” – Ernest Hemingway, “For Whom the Bell Tolls”

At this point in “For Whom the Bell Tolls,” the protagonist, Robert Jordan, is on the eve of a major battle and is having an inner debate about the act of killing. He is performing a Green Beret-type mission, where he is working with local indigenous people to take out a bridge during the Spanish Civil War just before WWII. He has discussed the act of killing with several of the locals that have been fighting there for a long time, and Robert Jordan is somewhat of a seasoned soldier himself. They all have different points of view, but the more senior of them tend to feel similarly: that killing is wrong, but sometimes necessary.

There is a certain naïvety around a society that is never willing to kill for any reason whatsoever, and those societies are usually built and protected by those who do the killing on their behalf. I have a great respect for pacifists who would die for their beliefs, but that sort of pacifism is a rare breed and most who claim such ideals simply have never been tested. Once they are hungry enough or their families are threatened, the heat of the moment — “the demon” — will take over and they will likely follow that same killer instinct buried deep within all of us.

However, just because a thing is necessary does not make it right, and therein lies the contradiction. It is wrong, but it is, at times, necessary. Those who would never in any conceivable way permit violence would allow rapists and murderers to do what they do. Non-lethal force is not always possible, and even the countries with the strictest weapon control laws know this, and have police forces on standby, armed to the teeth, for this reason.