According to averages in the USA, people in homes with handguns are twice as likely to be killed by a gun than people in homes without handguns.
The question is whether Christians can do more good in the world by killing, or more good in the world by laying down their lives.
It is harder to get statistics on worldwide efforts but I believe that Christians could save far more lives worldwide by not resorting to violence than by engaging in violence. But even if the statistics were not in our favor, I would still recommend nonviolence because I believe that God can bring about more good without Christians engaging in violence.
If Christians believed and practiced what Jesus taught, I don't think men like Hitler and Mussolini could have gotten a following.