Maybe I've got a different version of the Bible than other folks do. That's the only reason that I can think why people believe that, as a Christian, any taking of human life is wrong. Because in the version that I have, there were many instances in which God not only said that the taking of life was permissible but a command directly from Him!
Take the example of Deuteronomy 19 which goes into the requirements for cities of refuge within the new nation of Israel and how they are to be utilized in cases of manslaughter or murder.
“Now this is the case of the manslayer who may flee there and live: when he kills his friend unintentionally, not hating him previously ... he may flee to one of these cities and live; otherwise the avenger of blood might pursue the manslayer in the heat of his anger, and overtake him, because the way is long, and take his life, though he was not deserving of death, since he had not hated him previously.”
“But if there is a man who hates his neighbor and lies in wait for him and rises up against him and strikes him so that he dies, and he flees to one of these cities, then the elders of his city shall send and take him from there and deliver him into the hand of the avenger of blood, that he may die.”
Here we see that the “avenger of blood” was the proper one to whom a murderer should be delivered for execution.
Then there is the case that I am sure most of us have heard (Exodus 21:3) of the thief who is killed in the course of his thievery. The Bible declares that “...there shall no blood be shed for him.”
Now these are examples pulled from the Old Testament. Most folks seem to think for some reason that God was different back in Old Testament times, that he was bloodthirsty. I'm here to tell you that God is no different today than he was at any other point in the history of the world. Let's take a look at a New Testament example.
In Luke 22, Jesus has just told Peter that he would deny knowing Jesus. He then turns to the rest of his disciples and says, “When I sent you out without money belt and bag and sandals, you did not lack anything, did you?” His disciples replied, “No, nothing.” Jesus then says, “But now, whoever has a money belt is to take it along, likewise also a bag, and whoever has no sword is to sell his coat and buy one.”
Why would Jesus, a man who preaches peace, tell his followers “If you don't have a sword, sell some of your clothes and get one!” Well, first of all, while Jesus taught peace, he also said that he would not bring peace. “Do not think that I came to bring peace on the earth; I did not come to bring peace, but a sword.” As for why he told his followers to buy a sword, the answer is that he knew that the time of his betrayal was near and that the disciples were going to be scattered for a while. In the time that Jesus was referring to in the beginning of the quote, what has been called the limited commission, God had protected them as a way of showing his power, also providing food and shelter for the same reason. Now that God has proved his point, he will no longer be actively protecting and providing for them and they will need a means to protect themselves while out on their own. And the best tool for defending oneself from other men at that time was the sword.
You'll also notice that Jesus did not advocate his disciples disarming themselves and relying on Roman soldiers. The Romans were some tough cookies when it came to punishing lawbreakers but there were still plenty of people willing to risk that punishment for the quick payoff of crime. (Take Barrabas for instance.) On the flip side of that coin, he never advocated breaking of the Roman law either except when it flatly contradicted God's will.
Today, God still does not take an active role in providing for and protecting us. He has given most of us the ability to do these things for ourselves as well as commanded his followers to aid those who cannot do these things for themselves. And the best tool for defending ourselves today is the firearm.
And finally, note Romans 12:18: “If possible, so far as it depends on you, be at peace with all men.” The implied and unfortunate part of this is that there are some men who will not let you be at peace with them.